MEDICAL *SCH<S>L 
 
THE AMERICAN ANATOMICAL MEMOIRS 
 
 THE MORPHOLOGY AND EVOLUTIONAL 
 SIGNIFICANCE OF THE PINEAL BODY 
 
 BEING 
 
 PART I 
 
 OF 
 
 A CONTRIBUTION TO THE STUDY OF THE EPIPHYSIS 
 
 CEREBRI WITH AN INTERPRETATION OF THE 
 
 MORPHOLOGICAL, PHYSIOLOGICAL AND 
 
 CLINICAL EVIDENCE 
 
 FREP^RICK ITILNEY, M.D., PH.D. 
 
 PROFESSOR OF NEUROLOGY, COLUMBIA UNIVERSITY 
 AND 
 
 LUTHER F. WARREN, A.B., M.D. 
 
 PROFESSOR OF MEDICINE, LONG ISLAND COLLEGE HOSPITAL 
 
 1919 
 
 PUBLISHED BY 
 THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY 
 
 PHILADELPHIA 
 
(NJUO'< 
 
 ill 
 
 CONTENTS OF PART I 
 
 1. Introduction 5 
 
 2. Nomenclature 7 
 
 3. General review of the literature 9 
 
 4. The comparative morphology of the pineal region 17 
 
 1. In cyclostomes 21 
 
 2. In selachians 23 
 
 3. In ganoids ! 25 
 
 4. In teleosts 27 
 
 5. In dipnoi ; 29 
 
 6. In amphib : a 30 
 
 7. In reptilia ? 31 
 
 8. In aves 36 
 
 9. In mammals 37 
 
 5. The comparative embryology of the epiphyseal complex. 39 
 
 1. In cyclostomes 39 
 
 2. In selachians : 41 
 
 3. In ganoids 48 
 
 4. In telecasts 50 
 
 5. In amphibia 53 
 
 6. In reptilia .' 56 
 
 7. In aves 67 
 
 8. In mammals ' 72 
 
 6. The comparative anatomy and histology of the epiphyseal complex 80 
 
 1 . In cyclostomes 80 
 
 2. In selachians 92 
 
 3. In ganoids 98 
 
 4. In teleosts 103 
 
 5. In amphibia 114 
 
 6. In reptilia. 119 
 
 7. In aves 148 
 
 8. In mammals 155 
 
 7. Discussion 196 
 
 1. Significance of the pineal region 
 
 2. Evidence based on the gross morphology of the epiphyseal complex. ... 203 
 
 a. Phyletic constancy 203 
 
 6. Phyletic variation and morphologic specialization 205 
 
 c. Relative constancy of the epiphyseal complex with reference to 
 
 other structures of the pineal region 211 
 
 d. Relative constancy of the epiphyseal complex with predomi- 
 
 nance of the proximal portion 
 
 3 
 
4 . CONTENTS 
 
 e. The increase of the epiphysocerebral index during life in man.. 213 
 /. The resistance to the encroachment of the corpus callosum in 
 
 mammals 216 
 
 3. Evidence based on the histology of the epiphyseal complex 217 
 
 4. The relation of the parietal eye to the pineal body 226 
 
 5. The phylogenetic significance of the parietal eye with reference to 
 
 vertebrate and invertebrate 233 
 
 8. Summary and conclusions 238 
 
 9. Bibliography 240 
 
1. INTRODUCTION 
 
 "Son siege au milieu de parties tres-importantes de Pence- 
 phale, sa Constance chez Thomme et le vertebres, font pourtant 
 presumer que ses usages, s'ils ne sont pas d'un ordre aussi impor- 
 tant qu'on le supposait a Tepoque des Esprits Vitaux, n'en sont 
 pas moins reels et tres-interessant a connaitre." 
 
 Legros. These de Paris, 1873, page 24. 
 
 "Vix ulla unquam corporis nostri particula tantam famam 
 inter eruditos non modo, sed etiam inter illiterates nacta est, ac 
 cerebri sic dicta glandula pinealis." These words written by 
 Soemmering 359 in 1785 still hold true. Not only did this organ 
 attract much early medical attention, but its reputation was 
 extended by the metaphysicians and even 'further increased by 
 the satirical literature of an uncommonly virile period. Descartes 
 (1649) 89 in his discourse on the sources of the human passions, 
 expressed the belief that the pineal body was the seat of the soul. 
 This interpretation passed current during the epoch of Vital 
 Spirits. It did not, however, go altogether unassailed. Voltaire 411 
 so successfully made it the subject of parody that his whim- 
 sical conception of the pineal body became more influential than 
 the origina hypothesis of Descartes. According to Voltaire, 
 the epiphysis should be regarded as the driver which, by means of 
 two nerve bands, guides the action of the cerebral hemispheres. 
 These nerve bands were long referred to by the anatomists as 
 "the reins of the soul/' 
 
 During the past hundred years an increasing volume of re- 
 search has revealed the difficulties in the epiphyseal problem 
 and shown how far we are from a solution of it. In fact, the 
 views advanced by the students of this subject are so numerous 
 and often so divergent that any decision at the present time 
 
 5 
 
6 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 would seem ill-advised. The separation between those who 
 consider the pineal body a useless vestige and those who assign 
 to it extensive responsibilities in the sphere of internal secretion 
 is too great to be reconciled on any but the most careful investi- 
 gation of the grounds for their differences. The phylogenesis of 
 the organ among the vertebrates, especially in its relation to 
 the third or parietal eye, as well as the significance of the struc- 
 ture as a possible mark of identification in the line of evolution 
 from the invertebrate to the vertebrarte phylum, has raised many 
 perplexing questions. Although the researches of morphologists, 
 physiologists, and clinicians have established many significant 
 facts, it still remains to assemble this evidence as much in its 
 entirety as possible in order to furnish a satisfactory basis for 
 the discussion of the problem. 
 
 It is the purpose of this work to gather the recorded facts 
 concerning the pineal body and present them in several parts 
 under the following headings: 
 
 Part I. The morphology and evolutional significance of the 
 pineal body. 
 
 Part II. The physiology and pathology of the pineal body. 
 
 Part III. The clinical aspects of the pineal body. 
 
THE MORPHOLOGY AND EVOLUTIONAL SIGNIFICANCE 
 OF THE PINEAL BODY 
 
 The morphological problem of the epiphysis may be for.- 
 mulated in the following questions: 
 
 1. What is the significance of the pineal region in its relation 
 to the epiphysis? 
 
 2. Is the pineal body a vestige or is it an organ in some way 
 necessary to metabolism? 
 
 3. Does its structure furnish evidence of its function? 
 
 4. What relation does it bear to the third or parietal eye? 
 
 5. What is the phylogenetic significance of the parietal eye 
 with reference to the vertebrates and invertebrates? 
 
 Before submitting these questions to discussion, it seems 
 advisable to offer the evidence as much in extenso as is practi- 
 cable, having particular regard for historical sequence. 
 
 2. NOMENCLATURE 
 
 The pineal body was known to the Greeks and called by 
 them the <ro^a /aowtSes and KWVO.PLOV because of its conical 
 shape. It was also termed the epiphysis because of its relation 
 to the rest of the brain. Latin authors refer to it as the turbo, 
 corpus turbinatum, glandula turbinata, glandula piniformis, glan- 
 dula conoides, conarium, penis cerebri, and virga cerebri. 
 
 Because of its resemblance to a pine cone, it was called by 
 Chaussier 63 and Willis 429 the corpus pineale. It has been called 
 by the Germans the Zirbel and Zirbeldruse, a designation which 
 doubtless has led to the more or less general use at present of 
 the term pineal gland. Several of the early writers called it the 
 glandula superior in contradistinction to the pituitary gland 
 which was referred to as the glandula inferior. 
 
 Since all of these terms were, in the main, devised to meet the 
 conditions in man and the higher mammals, it might be expected 
 
 7 
 
8 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 that they would not prove wholly satisfactory for some of the 
 lower vertebrates. Earlier works on the pineal body, even 
 such as dealt with ichthyopsid and sauropsid forms, employed 
 the terms epiphysis and corpus pineale with so little discrimina- 
 tion that these definitions became rather vague. The com- 
 plexity of the structure in the lower reptiles, in amphibia, and in 
 fish is such that it may only in a very general way be denomi- 
 nated the epiphysis. In the first place, many of the forms just 
 mentioned present, instead of a single epiphyseal process, two 
 well-marked structures projecting dorsad from the roof of the 
 interbrain. Ontogenetically, both of these processes are con- 
 nected with the epiphyseal anlage, and yet if one of them were 
 called the epiphysis which should it be and by what term should 
 the other be designated? 
 
 In a certain respect the suggestion of Hill ('91) 179 to call one 
 process the anterior epiphysis and the other the posterior epiphysis 
 has much to recommend it on morphological grounds. Unfor- 
 tunately, connotation has so rigidly associated the term epiphysis 
 with the much altered and modified conditions as they occur in 
 man and mammals, as almost certainly to lead to confusion in 
 the broader application proposed by Hill. More available, 
 although not without their defects, are the proposals of Studnicka 
 ( J 96) 386 according to which the posterior epiphyseal process 
 becomes the pineal organ and the anterior process the parapineal 
 organ. The use of the term pineal at once reverts to the mam- 
 malian forms, for description of which it was first employed. 
 To apply this term, as, for example, in the fish where it has no 
 descriptive value, cannot be in accord with the best morphologi- 
 cal tendencies. Yet to Studnicka should be accredited the most 
 thorough and extensive consideration of this subject; his defini- 
 tions may, for this reason, be regarded as standards, especially 
 if the desire to avoid new terms is kept in mind. Accepting 
 Studnicka's terminology of an anterior process, the parapineal 
 organ, and the posterior one, the pineal organ, it is necessary to 
 recognize certain subdivisions in each of these organs. The 
 pineal organ has an end-sac, a stalk, and a proximal portion, the 
 latter in some cases is connected with the rest of the interbrain 
 
THE PINEAL BODY 9 
 
 by means of a short, slightly constricted piece, the peduncle. 
 The parapineal organ, likewise, has an end-sac, a stalk, and a less 
 well denned proximal portion. Much variation exists in the 
 forms presenting these several parts in many instances, one or 
 more of the parts described may be absent, yet, to make the 
 terminology as comprehensive as possible, all of these portions 
 should be included. Upon this basis the following constituents 
 may be recognized in the epiphyseal complex: 
 
 I. The pineal organ, consisting of: 
 
 1. An end- vesicle. 3. A proximal portion. 
 
 2. A stalk. 4. A peduncle. 
 
 II. The parapineal organ, consisting of: 
 
 1. An end- vesicle. 3. A proximal portion. 
 
 2. A stalk. 
 
 The proximal portion and peduncle of the pineal organ cor- 
 respond to the epiphysis or corpus pineale of mammalian anat- 
 omy. The proximal portion is probably analogous to the cellu- 
 lar part of the pineal body while the peduncle is comprised 
 largely of nerve fibers. 
 
 3. GENERAL REVIEW OF THE LITERATURE 
 
 Galen (1576) 138 gave a description of the conarium in its rela- 
 tion to the third ventricle as well as to the chorioid plexus and 
 blood vessels about it. According to his interpretation, the 
 organ serves as the support for the great vessels converging upon 
 that portion of the brain. Oribasius (1554) 285 mentioned but 
 did not describe the epiphysis. Uvarthonus 401 believed that 
 delicate nerve fibers enter the pineal body; these fibers seem to 
 take origin in the lower portion of the spinal cord. Bauhinus 
 (1616) 16 considered the conarium to be a glandular structure 
 related to the chorioid plexus. Diemerbroeck (1633) 91 showed 
 certain differences between the pineal body in man and in other 
 mammals. Dionis (1706) 93 described the pineal body as attached 
 upon either side to the chorioid plexus by a small band. This 
 band may be a nerve derived from the sympathetic system. 
 
10 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Duverney (1761) , 100 in support of the theory of Descartes (1649), 89 
 claimed that the pineal body did not exist in the dog. Vicq- 
 d'Azyr (178 1) 408 observed the epiphysis in man, but could not 
 find it in fish. Stannius 373 found it in all species which he ex- 
 amined and made a particular study of it in the salmon. In 
 this form he spoke of it as a highly vascular structure. Perrault 306 
 found the epiphysis in the ostrich. Borrich and Harder 38 
 observed the pineal body in the eagle. Malacarne 258 found the 
 epiphysis in birds as did Cuvier ('45). 77 Bichat (1802) 28 con- 
 sidered the pineal body a gland, and in it he found granules of 
 some calcareous substance. The general character of the 
 pineal body is something like the cortical substance of the brain. 
 Soemmering (1785) 359 gave an accurate account of the form of 
 the conarium and also its dimensions in man. In his descrip- 
 tion he confines himself largely to the fact that there occur in 
 the organ accumulations of a substance which he calls brain sand 
 or acervulus cerebri. Soemmering noted many different condi- 
 tions under which this brain sand was apt to collect in the dif- 
 ferent parts of the pineal body. Haller (1768) 165 believed the 
 concretions were pathological and related to mental disorders. 
 Many observers made mention of calcareous concretions in the 
 pineal body, among them being Saltzmann, Ruysch, Meibomius, 
 Vieussens, Vicq-d'Azyr, Malacarne, Brunner, Kruger, Bartholin, 
 Winslow, Petermann, and Santorini. Parisini 300 described the 
 pineal body in the camel, elephant, and lion, and Harder 170 gave a 
 description of it in the dog. Carus (1814) 59 described the epi- 
 physis as having the form of a small peeked sac with almost no 
 nerve fibers in it. He was unable to find the organ in the sal- 
 mon. Chaussier 63 described the form of the pineal body in some 
 mammals, suggesting that its shape compared to the pomme de 
 pin, which comparison led eventually to the adoption by the 
 French of the term corpus pineale. The Wenzels (1812), 42 in 
 their description of the pineal body, call attention to the fact 
 that the organ varies greatly in size according to the period of 
 life. Its size from the seventh year is augmented regularly 
 until middle life and then a successive diminution occurs until 
 old age. Acervulus cerebri is not found in the embryo nor in 
 
THE PINEAL BODY 11 
 
 the fetus, but after the seventh year of life this element makes 
 its appearance and tends to increase until old age. Cruveilhier, 72 
 in his description of the conarium, drew attention to a cavity 
 situated near the base of the structure which frequently con- 
 tained a fluid. Gratiolet, 157 referring to this cavity, described 
 it as the ventricle of the pineal gland. 
 
 Ma jen die, (1795) 257 commenting at considerable length upon 
 the hypothesis of Descartes concerning the seat of the soul, 
 ingenuously remarks that he himself has a better conception of 
 the nature and function of the pineal body which he desires to 
 substitute for the theory of Descartes. His own suggestion, 
 says Majendie, is not only very simple, but actual and true, for 
 it must be obvious from the situation as well as from the struc- 
 ture and form of the pineal body that it serves as a tampon 
 designed to expand and in this way to close off the aqueduct of 
 Sylvius or, at other times, shrinking, to permit this aqueduct to 
 open again so that the fluid in -the ventricles may have free 
 access from the third chamber to the fourth. Majendie, how- 
 ever, does not state upon what grounds the internal structure of 
 the pineal body justifies such a belief, but he is none the less 
 emphatic in calling attention to the valve-like nature of the 
 conarium with reference to the cerebrospinal fluid. 
 
 Gunz (1753) 161 attributed dementia to impeding of the flow of 
 spirits caused by the pineal body. Burdach ('19-'26) 4S con- 
 sidered the pineal body as supplementary to both the cerebellum 
 and cerebral hemispheres. Tiedemann ('23) 395 found the epi- 
 physis in reptiles, birds, and mammals. Serres ('24-'28) 353 and 
 Willis 429 both make the statement that the epiphysis occurs in 
 fish, birds, 'and reptiles in fact, in all classes of vertebrates. 
 Andral ('29) 4 also described the organ as occurring in all the 
 classes of vertebrates. Brandt ('29) 40 recognized a glandular 
 structure under a small scale in the head of Lacerta agilis which 
 corresponded to a circular depression in the parietal region of 
 the skull. This he regarded as a special gland. Milne-Edwards 
 ('29), 107 in his researches on lizards, figures but does not describe 
 certain plaques in the head of these animals. He indicates these 
 as the occipital plaque, the parietal plaque, and the interparietal 
 
12 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 plaque. The latter is a black spot corresponding exactly to the 
 position of the pineal gland. Duges ('29) 97 also figures the 
 same appearance in certain lizards. As early as 1835 Hollard 188 
 had made the observation that the epiphysis was entirely nerv- 
 ous in structure. He is also authority for the statement that 
 this body does not occur in fish. Gottsche ('35), 154 however, 
 states that the pineal body does exist in all fish. Valentin ('43) 403 
 concurred in Hollard' s idea, although he was of the opinion that 
 the elements in the pineal body differed considerably from the 
 gray matter of the brain. Guillot ('84) 16 makes the statement 
 that, although the pineal body exists in all vertebrates, it is not 
 until the reptiles are reached that the pineal apparatus makes 
 its appearance in most complete form. Reguleas ('45) 325 recog- 
 nized that in man the pineal body, both in its volume and form, 
 was variable. 
 
 . Observations concerning the structural character of the pineal 
 body were made at a remarkably early period. It was not, 
 however, until the methods of histological technique were fairly 
 well advanced that much attention was devoted to the minute 
 structure of the conarium. Kolliker ('87) 212 observed two 
 types of cells in the pineal body; that is, small round cells and 
 multipolar nerve cells with compact bundles of nerve fibers. 
 These latter were few in number. From his observation Kolliker 
 was led to believe that the pineal body is entirely nervous in type. 
 Clarke ('60) 69 found nerve fibers, nuclei, and brain sand but no 
 nerve cells in the pineal body. He also observed a reticular 
 structure which resembled the olfactory mucous membrane. 
 The arrangement of the cells, he believed, was similar to that of 
 the fourth layer of the olfactory bulb in sheep and cats. 
 
 Faivre ('55) 114 was among the first to make an extensive com- 
 parative histological study of the pineal body. He examined the 
 minute structure in man, horse, guinea-pig, dog, ox, rabbit, pig, 
 hen, turkey, dove, and tortoise. As a result of his observations, 
 he recognized three elements in the human pineal body: first, a 
 fibro vascular envelope; second, a globular parenchyma, and, 
 third, acervulus cerebri. Faivre is in general accord with 
 Valentin, in that the pineal body differs essentially from the 
 
THE PINEAL BODY 13 
 
 rest of the nervous system and has an appearance strikingly 
 ike the pituitary gland. He, apparently, was first to recognize 
 that the cells of the epiphysis contained granules in their cyto- 
 plasm. These he called parenchymal cells. He also observed 
 that these cells were smaller in childhood than in adult life and 
 concluded that the parenchyma of the pineal body is composed 
 of a large number of globules. The globules are generally 
 elliptical and irregular in shape. Faivre believed the globules 
 to be the nuclei of the cells, and to him must be accredited the 
 first observation of these cellular characteristics of the pineal 
 body. 
 
 Marshall ('61) 261 made some observations concerning size, 
 \veight, and sand-content in a chimpanzee. Schmidt ('62) 347B 
 showed the continuity of the epiphysis with the brain in the 
 human fetus and its relation as an evagination of the encephalic 
 roof. Stieda ('69) 376 studied the pineal body of birds and mam- 
 mals and described anastomoses of the cytoplasm of the cells 
 in the form of a reticulum. Luys ('65) 253 advances an ingenious 
 conception concerning the nature and connections of the pineal 
 body. In his opinion, this organ is a mass of gray substance 
 pertaining to the central gray matter surrounding the third 
 ventricle and having the same histological characters. He 
 claims that originally in the human embryo the structure is 
 bilobed like the mammillary bodies and that, therefore, it should 
 be considered as a transitory bilobed structure, a true posterior 
 mammillary body which has fused across the median line. Luys 
 concludes that the gray substance of the conarium, the hippo- 
 campal convolution, and the mammillary tubercles form with 
 the anterior pillars of the f ornix a complete system. The mammil- 
 lary bodies and the conarium are centers of reception for fibers 
 convergent from the hippocampal convolution. Efferently these 
 centers are connected with the optic thalami. Luschka ('67) 255 
 noted the presence of fibers in the pineal body of man. Frey 
 ('67) m believed that the pineal body was made up exclusively 
 of nerve tissue. He found in the adult the following elements: 
 1) multipolar ganglionic cells; 2) round cells with prolongations, 
 and 3) isolated nerve tubes. Leydig ('68) 232 states that the 
 
14 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 pineal body in the mouse resembles the pituitary body in reptiles 
 with certain small differences. Meynert (77) 271 expresses the 
 opinion that the parallelism between the pineal body and the 
 pituitary body is a mistaken idea. He believes that the epi- 
 physis should be considered a ganglionic derivative of the teg- 
 mentum. It contains two types of cells, namely, those with a 
 diameter of 15 micra and those with a diameter of 6 micra. The 
 pineal body, in Meynert's opinion, differs from other ganglia 
 only in the fact that the cells are very close together. Krause 
 (76) 218 observed in the pineal body nerve fibers having a double 
 contour. Henle (71) 171 described the parenchyma of the pineal 
 body as subdivided by fibrous processes called septa such as 
 occur in lymph glands. These divisions gave rise to more or 
 less independent follicles or acini varying in size from 6 micra to 
 30 micra in diameter. It was Henle's opinion that the pineal 
 body resembles more exactly lymph glands than any other 
 tissue in the body. Stieda ('65) 375 in several species of amphibia 
 observed an epithelial structure between the eyes in the frontal 
 region of the head which he called the frontal cutaneous gland. 
 Subsequent investigation revealed that this so-called cutaneous 
 gland was in fact a portion of the epiphyseal complex. Paw- 
 lowsky (74) 305 described fibers in the epiphysis which seemed to 
 be derived from the posterior commissure. Huxley (76) 191 
 described the pineal body in Ceratodus forsteri. In this form 
 it occurs as a slender, cylindrical body. Baudelot (70) 14 gave 
 a detailed description of the pineal body in Gadus merlangus. 
 He also found it in the salmon and in the Cyprinoids. Camper, 55 
 although he observed it in many fish, was not able to find it in 
 haddock or cod. Arsaky 8 was unable to detect the pouch of 
 the pineal body in fish. Haller (1768) 165 did not observe the 
 pineal body in birds nor did he observe it in the pike or trout. 
 He did find it, however, in the carp and tench. 
 
 Owen's ('81) 293 view of the conariohypophyseal organs is such 
 that it at least deserves comment, if only as a historical curiosity. 
 Accord'ng to Owen, the central nervous system in annelids forms 
 a ring through which passes the oesophagus (cesophageal ring). 
 In higher vertebrates, especially in embryonic life, the nervous 
 
THE PINEAL BODY 15 
 
 system manifests this same disposition, for here the brain curves 
 itself backward in such a way as to constitute a ring above the 
 region destined to become the mouth, thus producing a deep 
 fossa directed toward the brain. Owen regards this as part of a 
 canal which traverses the brain, now disposed as the cesophageal 
 ring of articulates. Early, however, the process is arrested and 
 the tube-like invagination comes to form the pituitary gland. 
 The original tube from the mouth region is completed by an 
 invagination from the dorsal region of the head which is con- 
 nected with the skin. This element becomes atrophic and its 
 remains constitute the pineal gland. Baraldi ('84) 13 modified 
 the theory of Owen by stating that the hypophysis was a deriva- 
 tive of the wall of the mouth of the gastrula or, in other words, 
 the last vestige of the extreme anterior portion of the alimentary 
 canal of worms. Robin's 334 idea seemed to offer some confirma- 
 tion to this opinion in the fact that he found in the epiphysis, 
 upon microscopic examination, a follicular, gray substance con- 
 taining a granular liquid very similar to that in the intestines. 
 Schwalbe ('81) 348 found medullated nerve fibers which ac- 
 company the blood vessels and come into relation with bipolar 
 and multipolar cells in the pineal body. He believes there 
 existed some similarity between the pineal body and lymph 
 corpuscles, but regards the cells of the former to be modified 
 epithelial elements. Ganser ('82) 142 thought the pineal body to 
 be an unpaired process of the ganglion habenulae. Flechsig 
 ('83) m maintained that the epiphysis sends fibers to the fascicu- 
 lus retroflexus. Sappey ('87) 344 considered the pineal body 
 analogous to the substance of the cerebral cortex. Mingazzini 
 ('89) 276 regarded the elements of the pineal body as similar to 
 those of the lymphatic corpuscles. Holler ('90), 278 investigat- 
 ing the epiphysis in the chimpanzee, distinguishes an unpaired 
 peduncle which constitutes the largest part of the pineal body. 
 The organ itself is 3 mm. x 2 mm. long. The peduncle is 4 mm. 
 long and consists of nervous tissue. The pineal recess is ex- 
 tensive. Moller regards the structure as a rudimentary organ 
 in a retrograde state. Charpy ('94) 62 considers the epiphysis as 
 a degenerating organ made up exclusively of epithelial elements 
 
16 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 and some nerve fibers. Debierre ('94) 84 believes the pineal 
 body to be a blood vascular gland with many degenerated 
 elements. Lotheissen ('94) 25 studying a large number of mam- 
 mals, recognized in marsupials (Macropus giganteus) some 
 fibers of the fasciculus retroflexus which penetrate the pineal 
 body, also some fibers which leave the summit of the epiphysis 
 which he believes represent the remains or rudiment of the 
 parietal nerve in reptiles. Cajal ('95) 53 thinks that the nerve 
 fibers in the pineal body are sympathetic and the body itself 
 is a blood vascular gland. Condorelli-Francaviglia ('95) 70 in 
 studying the brain of a marsupial (Halmaturus dorsalis), noted 
 in consequence of poor development of the corpus callosum that 
 the pineal body was only 2 mm. long and 1.5 mm. wide. Heitz- 
 mann ('96) 169B described the epiphysis as composed of gray 
 substance. Staderini ('97) 372 investigated the development in 
 many mammals. Soury ('99) 365 described connective tissue 
 septa dividing the pineal body into compartments which are 
 occupied by a second tissue resembling adenoid tissue in which 
 are round cells and cells with long prolongations. Bechterew 
 ('00) 20 found evidence of nerve fibers passing from the posterior 
 commissure to the peduncle of the pineal body. Zancla ('06) 432 
 studied the histology of the epiphysis in man. He observed 
 cells in the parenchyma which consist of a scant protoplasm and 
 large nuclei. These cells have a stellate form and prolongations 
 which often bifurcate at acute angles and then ramify still 
 further. The cells lie in a mesh of fibrils apparently nervous 
 in character. By the methods of Cajal, Weigert, and Biondi, 
 he was unable to interpret these cells either as nerve elements 
 or as glandular cells. He believed they are of a neuroglial 
 character and advances the hypothesis that they have an internal 
 secretory function. Around the calcareous concretions he found 
 necrobiotic areas. Romiti ('82) 336 studied the development of 
 the epiphysis in the rabbit. Anglade and Ducos ('08) 5 found 
 the organ made up mostly of neuroglia in man. 
 
THE PINEAL BODY 17 
 
 4. THE COMPARATIVE MORPHOLOGY OF THE PINEAL REGION ; 
 
 To make the proper evaluation of the pineal body this organ 
 should be considered in relation to its immediate encephalic 
 environment. Indeed, any study of the pineal organ which 
 omitted this environment would give but an inadequate view of 
 the epiphysis. A number of structures make ttieir appearance 
 in connection with the roof -plate of the forebrain. Some of these 
 have a marked constancy; some are transitory, making their 
 appearance in one or two classes of vertebrates only, yet all 'of 
 them have a definite, phylogenetic significance in connection 
 with the epiphyseal complex. Embryologically, the roof-plate 
 of the primitive forebrain vesicle, that is, the prosencephalon, 
 gives rise to a number of evaginations. Certain of these even- 
 tually become prominent, adult organs. The most conspicuous, 
 both because of its constancy throughout the phylum and 
 its numerous adaptations, is the pineal or epiphyseal complex. 
 It has been suggested that the structures which form the roof 
 of the interbrain be known collectively as the pineal region. 
 This suggestion made by Minot ('01) m offers a convenient term 
 for the identification of a complex area of the brain. According 
 to Minot, the pineal region begins at the lamina terminalis or 
 lamina neuroporica which is its cephalic limit and comprises the 
 following elements: 
 
 1. The paraphyseal arch. 
 
 2. The velum trans ver sum. 
 
 3. The post velar arch, also known as the dorsal sac. 
 
 4. The epiphysis, also known as the corpus pineale. 
 
 5. The posterior commissure. 
 
 Minot 's specification of the pineal region needs some extension 
 in order to meet the requirements of all classes of vertebrates. 
 The following description of the pineal region makes provision 
 for all of the elements which may and in some instances do 
 appear in this area of the brain. 
 
 Paraphysis. The paraphysis is an evagination situated at 
 the extreme cephalic end of the forebrain roof-plate. Ventrally 
 it is continued into the lamina neuroporica. Dorsally it is con- 
 tinuous with the velum transversum. Minot assumed that the 
 
 MEMOIR 9 
 
18 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 pineal region develops a series of structures which seem to be 
 directly concerned with the formation of the fluid in the cavities 
 of the brain. He holds that the chorioid plexus supplies the 
 main bulk of this fluid, but the gland-like organization of the 
 paraphysis indicates that it may supply a secretion of special 
 chemical substances to the encephalic fluid. The organ reaches 
 its highest degree of development in amphibia, where it becomes 
 a large, complicated, glandular structure with a central canal 
 from which a complicated set of anastomosing tubules are given 
 off. It has a well-marked sinusoidal type of circulation. These 
 conditions have been observed by Warren 416 in Siredon, Nec- 
 turus, Proteus, Siren, Ichthyophis, Triton, Rana, Amblystoma, 
 and Diemyctylus. The paraphysis has a well-developed, 
 glandular character in amphibians and lizards; in birds it is 
 reduced to a single, thick-walled outgrowth of small dimensions. 
 Selenka 352 in 1890 observed the organ in opossum; it has also 
 been observed by Warren ('17) 417 in the sheep, and also by 
 Francotte 127 in 1887 in the human embryo. The paraphysis is 
 much reduced in the upper and lower ends of the vertebrate 
 series, while in the middle, especially in amphibia, it is much 
 developed. In amphibia its character is glandular, as it is also, 
 to a less degree, in reptiles. 
 
 The paraphysis was erroneously regarded as the conarium by 
 Selenka ('90). 352 It has also been called the anterior epiphysis 
 by Burckhardt ('90) 42 and the pre-paraphysis by His ('68). 182 
 Sorensen ('94), 363 called it the posterior chorioid plexus. 
 
 The velum transversum. This is a transverse furrow, imme- 
 diately caudad to the paraphysis, which projects into the ventricle 
 and separates the paraphysis from the dorsal sac. In some 
 instances this furrow is simple and flat, but in others it is thrown 
 into many subsidiary folds and becomes highly vascular in the 
 form of a plexus. In some forms, as in Peiromyzon, it is alto- 
 gether wanting, and under such circumstances the paraphysis 
 passes over without sharp line of demarcation directly into the 
 dorsal sac. In Chimaera there is a lack of the velum and also 
 a small paraphysis so that the dorsal sac seems to pass over 
 into the lamina supraneuroporica without demarcation. In 
 
THE PINEAL BODY 19 
 
 Dipnoians the velum presents a pair of folds or it may develop, 
 as in certain amphibia, as an unpaired chorioid plexus. 
 
 The dorsal sac. This element of the pineal region was called 
 the Zirbelpolster by Burckhardt 42 in 1890, the parencephalon 
 by Kupffer 222 in 1887, and the post-paraphysis by Sorensen 362 
 in 1893. Goronowitsch ('88) 153 appears to be the first to apply 
 to it the term dorsal sac. This sac is a dilated vesicle usually 
 extending far above the roof-plate. In mammalia, however, 
 in those forms in which the corpus callosum has made its appear- 
 ance, the sac becomes much flattened and is difficult to recognize 
 because of the altered condition consequent upon the develop- 
 ment of the corpus callosum. The walls of the dorsal sac are 
 lined internally by ependymal cells. In many instances these 
 walls may be thin and definite or quite thick, containing many 
 folds which may or may not be vascular; in certain instances 
 these folds attain such a vascularity that they resemble a chorioid 
 plexus. 
 
 The pars intercalaris anterior. The more caudal portion of 
 the dorsal sac as it approaches the level of the roof-plate may 
 become much thickened and contain a dense mass of neuroglia 
 tissue. Usually this intercalated portion is not of any great 
 extent. It appears only in a few forms. 
 
 The commissura habenularis. This element was called by 
 Osborn 288 in 1884 the superior commissure and by Gottsche in 
 1835 154 the commissura tenuissima. It affords a connection 
 between the two ganglia habenulae. In some cases, as in Petro- 
 myzon, the connection established by this commissure is such as 
 to include the mass of the two ganglia in the general commissural 
 region. In the immediate neighborhood of this commissure and 
 coming into direct connection with it is often seen the ending of 
 the nerve from the parapineal organ. This is particularly the 
 case in Saurians, and it is by tnis means that the so-called parietal 
 nerve makes its connection with the brain. Its fibers may be 
 traced in some instances as far as the ganglia habenulae. 
 
 The epiphyseal complex. This complex comprises two distinct 
 elements, a pineal and a parapineal organ. The pineal organ 
 may consist of an end-sac or terminal vesicle, a stalk, a proximal 
 
20 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 portion, and a peduncle. In all probability the proximal por- 
 tion of the epiphyseal complex gives rise to the epiphysis cerebri 
 or what has been called the pineal gland. In some forms nerve 
 fibers have been found making their course through the stalk of 
 this pineal organ and have thus given rise to the term nervus 
 pinealis. The parapineal organ is the second, though less con- 
 stant, portion of the epiphyseal complex. When present, it also 
 consists of an end-vesicle, a stalk, and a somewhat dilated 
 proximal portion. Most of these evaginations contain cavities 
 which are in communication with the third ventricle. The 
 recess which connects the pineal organ with this ventricle is 
 known as the recessus pinealis. 
 
 . The pars intercalaris posterior. The caudal wall of the proximal 
 portion of the pineal organ often shows a marked increase in 
 thickness as it approaches the level of the diencephalic roof. 
 This thickening interposes an area between the proximal portion 
 of the pineal organ and the posterior commissure. Often this 
 intercalated part shows considerable dimensions. In the forms 
 in which it is most developed, the fibers of the pineal nerve may 
 be seen to enter this intercalated portion in the roof of the inter- 
 brain. It has been called the pars intercalaris by Burckhardt 
 in 1890, 42 but the necessity of designating it the posterior inter- 
 calated portion becomes obvious in view of the fact that an 
 anterior structure of like character has already been described. 
 
 The posterior commissure. The last and caudalmost struc- 
 ture in the roof of the interbrain is the posterior commissure. 
 This has already been assigned by Minot in 1901 277 to the mid- 
 brain, but the fact 'that certain fibers from the tractus pinealis 
 and the nervus pinealis may be traced into direct relation with 
 this commissure seems to ally it more with the derivatives of the 
 roof-plate in the interbrain region rather than that of the mesen- 
 cephalon. 
 
 The homology of all of these parts in the roof -plate of the 
 prosencephalon has been given for the different classes of verte- 
 brates by Burckhardt in 1890 42 in his work on Protopterus and 
 again in his work (45) on the structural plan of the brain. With 
 this view of the generalized plan of the pineal region in verte- 
 
THE PINEAL BODY 21 
 
 brates, it will now be possible to consider in detail some of the 
 variations which the region presents in the different classes. 
 
 1 . The pineal region in cyclostomes 
 
 In cyclostomes the absence of the velum transversum causes 
 the paraphysis to pass over into the dorsal sac without sharp 
 line of demarcation. In fact, it is difficult to make out. with 
 any degree of certainty a true paraphyseal process. What 
 there is of a paraphysis is a small evagination from the most 
 cephalic portion of the dorsal sac, and the morphological lines of 
 differentiation are such as to leave it still open to doubt whether 
 there is an actual paraphysis in these forms. Studnicka ('99) 388 
 is authority for the statement that such an organ does exist 
 in Petromyzon. In Ammoccetes the epiphysis is more clearly 
 defined. The lamina supraneuroporica in cyclostomes is more 
 specialized than in other vertebrates. In the most dorsal por- 
 tion of this membrane there occurs a thickening which lodges 
 fibers passing in a transverse direction and constitutes a com- 
 missure knbwn as the commissura pallii. The dorsal sac is un- 
 usually high and deflected in a cephalic direction as a result of 
 the pressure put upon it by the pineal and parapineal organs. 
 Its dorsocaudal wall shows a marked in vagina tion as a result of 
 the pressure not only of the epiphyseal complex, but also of the 
 ganglion habenulae. No chorioid plexus or other vascular for- 
 mation appears in direct connection with either the paraphysis 
 or the dorsal sac. The pars intercalaris anterior is absent, but 
 a very massive commissura habenularis is observed in all forms, 
 making its appearance early in the course of development. 
 
 The epiphyseal complex presents a pineal organ and a para- 
 pineal organ. Both of these lie in close apposition to each other 
 extending cephalodorsad in such a direction that their terminal 
 portions come to overlie the dorsal sac. The dorsal wall of the 
 pineal organ lies immediately beneath the frontal region of the 
 skull. The posterior intercalated portion is also absent, but a 
 large posterior commissure occurs in all forms. The pineal, as 
 well as the parapineal organ, possesses a nerve, that connected 
 
22 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 with the pineal organ, the so-called pineal nerve, ends in the 
 posterior commissure, while the parapineal nerve has its termi- 
 nation in the commissura habenularis. 
 
 Probably the first observation upon this region in the cyclo- 
 stomes was made by Serres 353 in 1825. Other contributions fol- 
 lowed by Schlemm and d'Alton 347C in 1838. Johannas Miiller 280 
 in 1838 and Siebold and Stannius 355 in 1854 added their studies 
 of this region. Mayer 265 in 1864 mentioned the occurrence of 
 
 Epid Cor 
 
 -.Sohd 
 
 JLs 
 
 Fig. 1 Schematization of pineal region in Cyclostomes, according to Stud- 
 nicka, 1905. 
 
 Ls., lamina terminalis ; .P/, paraphysis; Pp., parapineal organ ',Po., pineal organ; 
 Ha., habenular ganglion; Th., parapineal nerve; Ch., commissura habenularis; R., 
 recessus pinealis; Cp., commissura posterior; n., Npin., nervus pinealis. 
 
 many calcium corpuscles in and about the pineal organ. Wie- 
 dersheim 422 in 1880 spoke of the epiphysis as a small, saccular 
 body, but it was not until 1883 that Ahlborn 2 first described the 
 microscopic appearances of the epiphyseal complex in which 
 he was able to observe two superposed vesicles. Ahlborn, 
 however, did not interpret these two vesicles as independent 
 evaginations from the roof of the interbrain, but considered 
 them as subdivisions of the epiphysis. 
 
THE PINEAL BODY 23 
 
 Later, Beard ('87) 17 and Owsiannikow ('88) 295 following Ahl- 
 born's lead, both spoke of two epiphyseal vesicles. Studnicka 
 ('99) 388 and Kupffer ('94) 224 showed that these two vesicles were, 
 in fact, independent parts of the epiphyseal complex. Studnicka 
 called the anterior vesicle the parapineal organ and considered it 
 homologous to the parietal eye of reptiles. This he later con- 
 firmed in a subsequent work. Kupffer, however, saw in the 
 parapineal organ or parietal eye of reptiles the homologue of the 
 paraphysis in Petromyzon. Retzius ('95) 331B was the first to 
 employ the Golgi method in Petromyzon and Ammoccetes. 
 By this means he was able to demonstrate the nerve elements 
 of the stalk of these two epiphyseal organs. The finer structure 
 of the pineal and parapineal organs in Petromyzon marinus was 
 given by Leydig in 1853 231 and Studnicka in 1899, 388 while Johns- 
 ston in 1902 195 described these organs in Lampetra wilderi. 
 
 2. The pineal region in selachians 
 
 The pineal region in selachians is very similar to that of 
 Petromyzon with the exception that in the epiphyseal complex 
 the parapineal organ does not appear. The selachians are 
 remarkable for another fact, namely, that one member of this 
 class, Torpedo, develops no part whatsoever of the epiphyseal 
 complex; that is to say, both the pineal and parapineal organs 
 are wanting. 
 
 In Notidanus, Burckhardt in 1890 42 distinguishes the follow- 
 ing parts: At the dorsal extremity of a thickened and invagi- 
 nated lamina neuroporica there appears a slightly developed 
 paraphysis. Immediately following this in the roof-plate there 
 is a marked invagination defining the velum transversum, which 
 appears in these forms as a simple infolding of the roof-plate 
 without any vascular development. The dorsal sac presents 
 itself as a more conspicuous element in the roof of this species 
 than in the cyclostomes. There is no anterior intercalated 
 portion and the epiphyseal complex shows only the presence of 
 the pineal organ. A short pars intercalaris posterior has been 
 described followed by the posterior commissure. This descrip- 
 tion given by Burckhardt in Notidanus holds true for most of 
 the forms of selachians with the exception of Torpedo. 
 
24 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 d'Erchia ('96) 109 differentiated in Pristiurus the same elements 
 as in Notidanus, but in Torpedo he found that the epiphyseal 
 complex was entirely wanting. He further observed that the 
 development of the velum transversum occurred much earlier 
 than the pineal organ. Minot ('01) 277 maintained that an actual 
 paraphysis does not develop in selachians. In comparing the 
 pineal regions of cyclostomes with selachians, the most striking 
 
 po 
 
 Ls 
 
 Fig. 2 Schematization of pineal region in Selachians, according to Studnicka 
 1905. 
 
 Ls., lamina terminalis; P/., paraphysis; V. velum transversum; Ds., dorsal 
 sac; Po., pineal organ; St., stalk of pineal organ; Ch., commissura habenularis; 
 R., recessus pinealis; Cp., commissura 'posterior; Sch., pars intercalaris posterior; 
 Prox., proximal, portion; Tp., tractus pinealis. 
 
 differences appear to be in the extreme development of the 
 parapineal and pineal organs in Petromyzon and . allied forms, 
 while the parapineal organ is absent in selachians. Further- 
 more, the absence of any distinct velum transversum in cyclo- 
 stomes makes the presence of a definite paraphysis extremely 
 doubtful, while the velum transversum in selachians differen- 
 tiates very clearly a fairly well formed paraphysis. The pineal 
 region in Elasmobranchs is much shorter than in Petromyzon. 
 
THE PINEAL BODY 25 
 
 Of the early workers upon the selachian pineal region, Jack- 
 son and Clarke (75) 193 appear to be the first to make mention of 
 the actual pineal organs as they occur in these forms. They 
 described this region in the brain of Echinorhynus spinosus. 
 According to their description, the structure was a small pro- 
 jection extending frdm the roof of the interbrain to the surface 
 of the skull. Ehlers 108 in 1878 gave the first detailed description 
 of the relation of these parts in Acanthias and Raia. Balfour 
 ('78) 10 in the same year described the embryological development 
 of the pineal region in selachians. Cattie ('82) 60 gave the de- 
 scription of the pineal organ in a large number of Elasmobranchs. 
 Carrington ('90) 58 described the organ in Lamna cornubica and 
 Galeotti ('96) 14 employing certain cytological methods in his 
 investigations of the pineal region, gave an important description 
 of these parts from a histological point of view. d'Erchia's 
 work on Pristiurus and Torpedo has already been referred to. 
 His was the notable observation that the epiphyseal complex 
 was entirely absent in Torpedo. 
 
 3. The pineal region in ganoids 
 
 This region in ganoids is characterized by the presence of the 
 usual elements with the exception that the parapineal organ does 
 not develop. In Amia alone is there any rudiment of an anterior 
 portion of the epiphyseal complex, and even here it is so slight 
 as hardly to justify the attempt to homologize it with the para- 
 pineal organ in Petromyzon. Goronowitsch ('88) 153 and Kupffer 
 ('93) 223 described the pineal region in Acipenser and recognized 
 in it all of the parts usually observed in this area of the brain. 
 Following a broad lamina supraneuroporica there is a well- 
 marked paraphysis which at first is truly membranous but subse- 
 quently becomes highly vascular and takes on the form of a 
 tubular gland eventually concealing the great part of the lamina 
 terminalis. In certain forms, as in Polyodon, the paraphysis, 
 although well developed, is relatively much smaller than in 
 Acipenser. The next element in the forebrain roof, namely, 
 the velum transversum, is broad and much convoluted although 
 not very highly vascular. The dorsal sac presents the form of a 
 
26 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 large evagination, generally membranous, and in several forms 
 having marked prolongations. Thus in Amia there are two such 
 prolongations, the more dorsal of which extends as far back as 
 the midbrain, while in Polypterus a prolongation of the dorsal 
 sac arches over the midbrain and extends as far caudad as the 
 cerebellum. No anterior intercalated part is present in the 
 ganoid, but a well-marked habenular commissure is present 
 immediately cephalad of the epiphyseal complex. This latter 
 consists of a single evagination from the roof-plate. The anterior 
 epiphyseal element is absent in the ganoid so that the pineal 
 organ alone is encountered in this region. Immediately follow- 
 ing the latter structure is a short pars intercalaris posterior and 
 then a large posterior commissure. 
 
 The pineal region in ganoids differs from that in selachians 
 mainly in the presence of a large and glandular paraphysis; also 
 in the existence of an unusually large and extensive dorsal sac, 
 prolongations of which are apt to extend far beyond the usual 
 limits of this structure, even arching over the midbrain and 
 reaching the cerebellum. 
 
 Of the early works upon ganoids, Salensky 341 in 1881 first 
 gave a description of the development of the pineal region in 
 Acipenser. Accounts of the ontogenesis in this same form were 
 later given by Owsiannikow ('90) 297 and Kupffer ('93). 223 Bal- 
 four and Parker ('82) 12 gave a description of the development of 
 this region in Lepidosteus. Hill ('94) 18 contends that there are 
 two epiphyseal outgrowths from the roof of the interbrain in 
 Amia calva. The more anterior of these two outgrowths or 
 vesicles, Hill thinks, is homologous with the parietal eye of 
 Lacertilia, and he further maintains that it is extremely prob- 
 able that the two vesicles in their primitive position were side by 
 side, thus indicating the existence of two organs which in the 
 primitive form, like the lateral eyes, were arranged as a pair for 
 some definite function. Eycleshymer and Davis ('97) 113 con- 
 firmed the findings of Hill and added the further important 
 observations that in the late embryonic state nerve fibers could 
 be seen connecting the commissure habenularis with the para- 
 pineal as well as the pineal organ. 
 
THE PINEAL BOD Y 27 
 
 4. The pineal region in teleosts 
 
 In teleosts the parapineal organ does not appear and the 
 pineal organ itself is present only in a seemingly retrogressive 
 condition. During the early stages of development, however, 
 in a few forms there is an anlage of the parapineal organ. The 
 lamina supraneuroporica is, if anything, more broad and more 
 pronounced than in the ganoids, but it differs from this structure 
 in the latter forms in the fact that it is not vascular nor does it 
 come into relation with any vascular network. A paraphysis 
 does not develop, as a rule, or if it does occur, it only appears 
 as a small evagination from the roof-plate, as in Belone acus. 
 Not infrequently in the earlier stages of development in Lophius, 
 the paraphysis appears as a small bud in the roof region. In 
 the larval forms of some species, as, for example, Anguilla and 
 Cepola, the paraphysis has the form of a very small evagination 
 from the roof consisting of a thin wall, but is not vascular and 
 in no way connected with a vascular net. The velum trans- 
 versum is a simple, flat, transverse fold which is not in connec- 
 tion with the chorioid plexus in any portion. In certain in- 
 stances this element is very little developed and may, in a few 
 cases, be entirely absent. The dorsal sac is, as a rule, very large 
 and presents itself in several different forms. Frequently it is 
 thrown into many folds, particularly the portion representing 
 the superior wall and in these folds are found numerous blood- 
 vessels in a plexiform arrangement. Sometimes the sac along 
 its caudal wall is grooved in the midsagittal plane and in this 
 groove rests the stalk of the pineal organ. An anterior inter- 
 calated portion is absent, but a well-marked habenular com- 
 missure is always observed. Following this commissure is the 
 pineal organ and caudal to it a short pars intercalaris posterior 
 followed by the posterior commissure (fig. 3). 
 
 Among the early workers in this region in teleosts are listed 
 some of the great pioneer names in morphology. Albrecht 
 Haller in 1768 165 described the epiphysis in the carp, but did 
 not find it in the trout. Cuvier in 1845 77 also observed it in 
 teleosts, and Carus in 1814 59 found it to be a saccular formation 
 extending from the dorsal .region of the brain. Tiedemann 39 ^ 
 
28 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 in 1816 could not find it in the bony fish, while Gottsche 154 in 
 1835 found it in these animals, but thought that it was connected 
 by blood vessels or a membrane with the ganglion habenulae 
 and the commissura habenularis. Mayer in 1864 265 gave a 
 description of the epiphysis as being merely a vascular convolu- 
 tion in the roof of the interbrain, while Owen 294 in 1866 was not 
 at all sure of its existence even as a vascular convolution of the 
 roof-plate. In 1870 Baudelot 14 described the epiphysis as a 
 
 -Af 
 
 7>- Sc/t Cp 
 
 Fig. 3 Schematization of pineal region in Teleosts, according to Studnicka, 
 1905. 
 
 Ls., lamina terminalis; P/., paraphysis; Ds., dorsal sac ; V., velum trans versum; 
 Ch., commissura habenularis; Po., pineal organ; St., stalk of pineal organ; Tp., 
 tractus pinealis; Sch., pars intercalaris anterior; Cp., commissura posterior; M. 
 midbrain. 
 
 round or pear-shaped body between the lobi optici. The first 
 exact description of the organ was given by Rabl-Riickhard 319 
 in 1883 on the basis of microscopic sections. Cattie 60 in 1882 
 described the gross appearances of the organ in a large number of 
 teleosts, and Hill 180 in 1894 gave one of the most detailed and 
 reliable accounts of this region in teleosts, basing his description 
 on his findings in salmon. Other excellent descriptions of the 
 organ in teleosts have been given by Ussow ('82), 402 Leydig 
 ( ? 96), 239 and Handrick ('01). 168 
 
THE PINEAL BODY 29 
 
 The work of Galeotti 140 in 1896 on these forms is of particular 
 interest. This observer, applying certain means of cellular 
 differentiation in the -technique, showed that some cells of the 
 pineal organ give definite evidence of secretory activity. In 
 Leuciscus he found that the nuclei of the cells contained fuch- 
 sinophile granules and also that the nucleoli in these nuclei 
 were often extruded and later appeared in the protoplasm of the 
 cells. The product of such secretion in Galeotti' s opinion was 
 delivered to the cavity of the organ. 
 
 The chief difference between the pineal region in ganoids and 
 teleosts lies in the fact that in the latter forms the paraphysis is 
 entirely absent while in ganoids it constitutes a conspicuous 
 element. 
 
 5. The pineal region in dipnoi 
 
 In dipnoi the only portion of the epiphyseal complex which 
 develops is the pineal organ and this is much less well defined 
 than in the lower forms. No anlage of the parapineal organ 
 makes its appearance. The paraphysis develops later than the 
 pineal organ. The lamina supraneuroporica, according to 
 Burckhardt ('90), 42 as it appears in Protopterus, is very thick 
 and well developed. The absence of any well-defined velum 
 transversum makes it appear as if the paraphysis were an an- 
 terior division of the dorsal sac, and yet a paraphysis may be 
 said to exist in these forms, although no sharp line of demarca- 
 tion may be drawn between it and the dorsal sac. The para- 
 physis itself presents a number of transverse folds beginning in 
 the attenuated membrane immediately dorsal to the lamina 
 supraneuroporica. In Ceralodus the entire paraphysis has the 
 appearance of a glandular structure, the lumen of which is in 
 connection with the ventricle of the brain by means of a small 
 canal. Although an actual velum transversum does not, in the 
 strict sense, exist, Kerr ('03), 202 in Lepidosiren, and Studnicka 
 ('95, '96), 386 in Ceratodus, have both described several folds in a 
 position dorsal to the paraphysis. The dorsal sac is but little 
 developed, although it does appear as a membranous structure 
 extending from the roof of the interbrain. No pars intercalaris 
 
30 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 anterior is observed, but there is a well-marked commissura 
 habenularis as well as the pineal organ, a posterior intercalated 
 portion, and the posterior commissure. 
 
 The earliest work upon this region of the dipnoi was by 
 Huxley 191 in 1876. In this he described the pineal organ as a 
 cylindrical structure which had a cordiform enlargement at its 
 distal extremity. This latter lay deeply seated in a small exca- 
 vation of the cartilaginous skull roof. Wilder 427 in 1887 showed 
 an unusually large paraphysis in Ceratodus, but did not observe 
 the pineal organ. Sanders 343 in 1889 saw the end^ vesicle of the 
 pineal organ in the form of a small body situated above the 
 chorioid plexus of the interbrain. Studnicka ('95, '96), 386 
 distinguished in Ceratodus a dorsal sac and a paraphysis, the 
 former lying closely compressed against the latter. He also 
 observed a pineal organ with a long stalk which lies in a fold 
 along the superior wall of the dorsal sac, while the end-vesicle 
 is situated above the paraphysis. In Protopterus annectens, 
 Wiedersheim ('80) 423 and Beauregard ('81) 19 mistook the dorsal 
 sac for the pineal organ, and Fulliquette ('86) 132 was unable to 
 distinguish between the ganglion habenulae and the pineal 
 organ. The erroneous identifications made by these authors go 
 to show the great difficulties which the pineal region in dipnoians 
 presents. It was not until 1890 and 1892 that Burckhardt 42 " 44 
 first gave the proper description of the pineal organ in these 
 forms. 
 
 6. The pineal region in amphibia 
 
 In Urodela and Apoda only the pineal organ develops and 
 this in but an extremely rudimentary form. The portions of the 
 pineal organ which are present in these forms represent the 
 proximal part of that structure. In no other group of verte- 
 brates is the pineal organ so little developed; it presents itself as 
 a sac lying close to the interbrain, the lumen of which is sub- 
 divided into numerous branches. deGraaf 155 in 1886 was first 
 to recognize this condition and describe it in amphibia. 
 
 In Anura, as in Urodela and Apoda, the pineal organ only 
 develops. It usually consists of the proximal saccular part of 
 
THE PINEAL BODY 31 
 
 this structure and the end-vesicle. The latter constitutes the 
 cutaneous gland. These two parts, connected by a stalk of fine 
 fibers which lead to the brain roof as the tractus pinealis, are the 
 distinguishing features of this region in Anura. The proximal 
 part alone in Anura is the homologue of the very rudimentary 
 organs observed in Urodela. The pineal organ of the frog's 
 brain has often been mistaken for the highly developed chorioid 
 plexus, for the paraphysis, or for the dorsal sac. Such errors 
 have been made by Wymann 431 in 1853, Reissner 328 in 1864, and 
 Stieda 379 in 1875. Goette 151 in 1873 first recognized the proximal 
 portion of the pineal organ and called it the epiphysis. This he 
 observed in the early stages of development in Bombinator. 
 Gravenhearst 158 many years before this found the distal part of 
 the pineal organ in the head of Rana subsaltans, situated in 
 relation to a light colored spot on the skin over the head. Reiss- 
 ner 328 also noted a similar spot. Stieda called this spot the 
 Scheitelfleck (parietal spot). To this spot he gave an inter- 
 pretation of much interest, for he believed that it marked the 
 situation of a peculiar, subcutaneous frontal gland directly under 
 the skin and this gland, therefore, became known as the frontal 
 subcutaneous gland of Stieda. A fine, thread-like structure led 
 from the skull to this gland and thus connected them. Ciaccio 65 
 in 1867, following Stieda's lead, placed this structure among the 
 so-called nerve glands of Luschka. Leydig 233 in 1856 considered 
 the organ merely as a skin gland, but Goette 151 in 1873-75 studied 
 the epiphysis development ally and stated that the subcutaneous 
 frontal gland was nothing more than the detached distal end of 
 the epiphysis. 
 
 The pineal region in amphibia, generally speaking, comprises 
 the following structures: The lamina supraneuroporica, which 
 is a short and thick end wall of the forebrain. The next and, 
 perhaps, most conspicuous element of the pineal region in am- 
 phibia is the massive and vascular paraphysis which, according 
 to certain authorities, reaches its highest development in these 
 forms. It has all the characteristics of a tubular gland with a 
 definite sinusoidal circulation and a canal which connects it with 
 the ventricles of the brain. The velum trans versum is short 
 
32 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 and plexiform, in many forms attaining a marked vascularity. 
 The next structure in the pineal region is the commissura habenu- 
 laris, following which is a long pars intercalaris anterior. Then 
 follows the epiphysis or the proximal portion of the pineal organ 
 with a marked pineal recess. There can be little doubt that 
 this particular form in which the pineal organ presents itself 
 is the actual proximal part of other species. Following the 
 epiphysis is a thick pars intercalaris posterior, and finally the 
 posterior commissure. 
 
 Npm 
 
 M 
 
 Fig. 4 Schematization of the pineal region in Amphibia, according to Stud- 
 nicka, 1905. 
 
 Ls., lamina terminalis; P/., paraphysis; Ds., dorsal sac; Ch., commissura ha- 
 benularis; Po., pineal organ; Npir^, nervus pinealis; Ep., proximal portion pineal 
 organ; Tp., tractus pinealis; Sch., pars intercalaris posterior; Cp., commissura 
 posterior; M .., midbrain. 
 
 7. The pineal region in reptiia 
 
 In Prosaurians and Saurians, as in Petromyzon and some 
 teleosts, both the pineal and parapineal organs make their appear- 
 ance, but the order which they hold in the lower forms is some- 
 what reversed here since the parapineal organ gives rise to an 
 eye-like structure called the parietal eye. This parietal eye, 
 however, is present only in the lower reptiles. The pineal organ, 
 
THE PINEAL BODY 33 
 
 on the other hand, in most forms presents a less well-developed 
 appearance, and in many instances (in Lensu stricto) an epi- 
 physis cerebri alone may be observed. The parietal eye, earlier 
 but incorrectly called the pineal eye, is absent in many 
 forms even among the lower reptiles. It is undoubtedly the 
 homologue of the anterior epiphyseal organ or parapineal organ 
 of teleosts and perhaps the parapineal organ of Petromyzon. 
 No chapter in the morphology of the pineal organ is more 
 replete with interest or full of ..incentive to further research than 
 that dealing with the remarkable conditions observed in this 
 region of the brain in reptilia. From the observations on the 
 Saurians and Prosaurians have come far-reaching theories into 
 the phylogenesis of the vertebrates as well as many illuminating 
 efforts to trace the evolution of this phylum by means of the 
 unpaired parietal eye back to the invertebrates. Brandt 40 in 
 1829 was first to mention the presence of the epiphysis in the 
 Saurian brain. Milne-Edwards 107 and Duges 97 both in 1829 
 referred to certain scales in the head of Lacerta. Neither of 
 these authors described the structures, but their illustrations 
 plainly indicate that they had perceived the area in the skull in 
 which the parietal eye comes to the surface. Cuvier 77 and 
 Tiedemann 395 had both observed the organ in reptiles. Ley dig 234 
 in 1872 studied the embryo of Lacerta and Anguis, giving partic- 
 ular attention to the parietal region of the skull. He described 
 a peculiar body made up of long, epithelioid, and cylindrical 
 cells. These cells were so arranged as to form a rim, the border 
 of which comprises cells of a deep black pigment. This organ 
 was not, as one might think, the epiphysis, for this latter struc- 
 ture lies distinctly above the organ described by Leydig. Ley- 
 dig, furthermore, mentioned a parietal foramen and a spot on 
 the skull indicating the position of the organ which lies beneath 
 it. This structure Leydig called the frontal organ, and while he 
 strongly suspected that it was possessed of sensory function, he 
 did not commit himself to such a theory at the time in which he 
 wrote. Strahl 382 in 1884 thought that this frontal organ of 
 Leydig had certain relations to the epiphysis and seemed able to 
 demonstrate that Leydig's organ was nothing more than a 
 
 MEMOIR NO. 
 
34 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 detached distal portion of the epiphysis, the homologue of the 
 frontal gland in amphibians. The idea advanced by Strahl was 
 subsequently confirmed by Hoffmann 186 in 1886 and again by 
 Beraneck 21 in 1887. But it is to deGraaf 155 that we are indebted 
 for the first demonstration that the organ of Leydig was pro- 
 vided with a lens and a retina and was, hence, a real visual organ. 
 This work of deGraaf in 1886 was almost simultaneously con- 
 
 Fig. 5 Schematization of the pineal region in Sphenodon, according to Stud- 
 nicka, 1905. 
 
 Ls., lamina terminalis; V., velum transversum; P/., paraphysis; Ds., dorsal 
 sac; Ch., commissura habenularis; Pa., parapineal organ; Npar., nervus parapi- 
 nealis;Po., pineal organ; Ep., proximal portion pineal organ; Tp., tractus pinealis; 
 Sch., pars intercalaris posterior; Cp., commissura posterior; M., midbrain, Np., 
 accessory parapineal organ; R., Recessus pinealis. 
 
 firmed in the same year by Spencer 366 who carried on a large 
 number of observations upon many different Saurian forms, 
 confirming in detail the proposition advanced by deGraaf that 
 the structure described by Leydig as the frontal organ contained 
 not only a lens, but a definite retina. These works led up to 
 the later investigations on the parietal eye and also on what has 
 been called the third eye of vertebrates. 
 
THE PINEAL BODY 
 
 35 
 
 The parietal eye which occurs in many forms of Lacertilia is, 
 on the other hand, entirely absent in Ophidians, Chelonians, and 
 Crocodilians. In all reptiles, with the exception of Lacertilia, 
 the epiphyseal complex is so rudimentary that only the proximal 
 portion of the pineal organ remains. Indeed, in Crocodilia even 
 this is said to be absent. 
 
 is. 
 
 Fig. 6 Schematization of the pineal region in Ophidia, according to Studnicka, 
 1905. 
 
 Ls., lamina terminalis ; P/., paraphysis; V., velum trans versum; Ds., dorsal 
 sac; Ch., commissura habenularis ; Ep., proximal portion of pineal organ (epiphy- 
 sis); Cp., posterior commissure. 
 
 Burckhardt 45 in 1893 gave the first description of the pineal 
 region n the brain of Lacerta. He described a thin and flat 
 lamina supraneuroporica above which arose, to a considerable 
 height, a simple tubular paraphysis. In adult animals, as a 
 rule, this structure has the form of a thin-walled sac lined by 
 cuboidal ependymal cells. The paraphysis at first is without 
 vascularization, but later, by the ingrowth of blood vessels, it 
 becomes highly plexiform in character; yet in no instance is it 
 comparable to the vascularity observed in Amphibians. The 
 distal extremity of the paraphysis is flexed dorsally and often 
 
36 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 comes in contact with the ventrally flexed distal extremity of 
 the parietal eye. The velum transversum is well developed and 
 is plexiform in character, being highly vascular in structure. 
 Following the velum transversum is a dorsal sac usually, how- 
 ever, less conspicuous than the paraphysis and oftentimes smaller 
 than that organ. The commissura habenularis follows and is 
 in connection with two symmetrical ganglia habenulae. A pars 
 intercalaris anterior is not observed. 
 
 The epiphyseal complex has a different arrangement in the 
 several different classes of reptilia. In most Lacertilia the part 
 which seems to be the homologue of the parapineal organ has 
 become converted into a definite parietal eye with lens, retina, 
 and nerve of its own. The pineal organ, on the other hand, is 
 much reduced and appears but a remnant of the homologue of 
 this structure in some of the lower forms. In the orders of 
 reptilia, other than Lacertilia, the parapineal organ does not 
 develop and the pineal organ itself is reduced to a mere rudiment, 
 being represented wholly by the development of its proximal 
 portion. A short pars intercalaris posterior follows the epi- 
 physeal complex while a relatively large posterior commissure 
 forms the caudalmost structure in the roof of the interbrain. 
 
 8. The pineal region in aves 
 
 In birds, only the proximal portion of the pineal organ, the 
 part usually called the epiphysis or corpus pineale, develops. 
 It usually appears as a small circumscribed sac connected with 
 the roof of the interbrain or else it has a definitely glandular 
 structure with acini of varying size. Mihalkovicz 274 in 1874-77 
 studied the epiphysis in Meleagris gallopavo and in this bird 
 called attention to the definite follicular and glandular char- 
 acter of the tissue. Mihalkovicz' description is the most com- 
 plete concerning the epiphysis in birds. Galeotti 140 in 1892 
 added some details to Mihalkovicz' description of this struc- 
 ture and confirmed the opinion that it was glandular in its nature. 
 The pineal region in birds is compressed cephalodorsad because 
 of the marked development of the hemispheres and the cere- 
 
THE PINEAL BODY 
 
 37 
 
 bellum. This region contains in more or less rudimentary form 
 the following structures: A paraphysis, a very simple velum 
 transversum, a small and compressed dorsal sac, a commissura 
 habenularis, an epiphysis, undoubtedly the homologue of the 
 proximal portion of the pineal organ with a definite pineal recess 
 and a pineal peduncle, a pars intercalaris posterior of varying 
 size depending upon the species, and a fairly well-marked pos- 
 terior commissure. The relation of the epiphysis to the brain 
 roof in birds is different from that encountered in any of the 
 
 Ls - ^ , 
 
 Ch C'p - 
 
 tL 
 
 Fig. 7 Schematization of the pineal region in Aves, according to Studnicka, 
 1905. 
 
 Ls., lamina terminalis; P/., paraphysis; Ds., dorsal sac; Ch., commissura 
 habenularis; Ep., proximal portion of pineal organ (epiphysis); Cp., posterior 
 commissure; M., midbrain. 
 
 lower forms in that here the axis of the organ is at right angles 
 to the roof, whereas, lower in the scale the tendency has been 
 for the body to show a definite anterior or ventral flexion. 
 
 9. The pineal region in mammals 
 
 This region is made up as follows in the mammal: Following a 
 thin lamina supraneuroporica there occurs, according to Fran- 
 cotte 129 in 1894 in the early stages of development in the human 
 embryo, a short tubular process which he terms the paraphysis. 
 
38 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 d'Erchia ('96) 109 found this structure only as a simple fold in 
 the embryo, while recently Warren ('17) 417 has identified a small 
 but solid protuberance at the anterior extremity of the inter- 
 brain roof-plate in the human embryo which he believes is the 
 anlage of the paraphysis. This, however, soon disappears, leav- 
 ing no trace of its presence, although there develops in the 
 neighborhood of its origin certain prolongations which Warren 
 has described as the diencephalic prolongations. In the adult 
 brain of other mammalian forms no paraphysis has been ob- 
 served. The velum transversum, if present at all, has been 
 observed in the early embryonic period only and then as a simple 
 fold. This statement is based on the observations of d'Erchia. 
 The dorsal sac, because of the much-altered condition in the 
 mammalian brain due to the development of the corpus callosum, 
 has become much flattened and reduced to the level of the general 
 plain of the roof-plate. It has undergone further change in the 
 fact that it has acquired a rich vascularization and become 
 definitely plexiform, giving rise to the tela chorioidea superior 
 of human anatomy. The caudalmost portion of the dorsal sac 
 immediately in front of the epiphysis is elevated and pushed 
 back over the dorsal surface of the pineal body in such a way as 
 to form a thin, roofed sac whose ventral wall lies upon the dorsal 
 surface of the epiphysis. This is the recessus suprapinealis 
 described by Reicher^ 326 in 1859. A commissura habenularis is 
 the next element in the roof-plate, and this is situated in relation 
 with the peduncle of the epiphysis. The epiphysis in mammals 
 undoubtedly represents the proximal portion of the pineal organ. 
 The epiphysis itself is a solid, more or less conical shaped body 
 connected with the roof of the brain by one or more sets of 
 so-called peduncles. As a result of the development of the 
 corpus callosum, the epiphysis has gradually been brought to 
 assume a position which brings it into relation with the superior 
 colliculi of the midbrain. Situated between the epiphyseal 
 peduncles there is a small pineal recessus. The entire epiphysis 
 is located in a position much removed from the inner surface of 
 the skull. 
 
THE PINEAL BODY 
 
 39 
 
 M 
 
 Fig. 8 Schematization of the pineal region in Mammals, according to Stud- 
 nicka, 1905. 
 
 Ds., dorsal sac; Ch., commissura habenularis; R., recessus pinealis; Ep., proxi- 
 mal portion of the pineal organ (epiphysis); Cp., commissura posterior; M., 
 midbrain. 
 
 In the light of the phyletic review just given concerning the 
 structures constituting the pineal region, it becomes clear that 
 any satisfactory consideration of the epiphyseal complex must 
 take into account the characters of the parapineal organ as 
 well as those of the pineal organ. It seems advantageous to 
 discuss the comparative embryology of these two parts and 
 then to consider the phyletic characteristics of each of them 
 separately. In this way the modifications of each organ may be 
 followed consecutively from one order to the next. 
 
 5. THE COMPARATIVE EMBRYOLOGY OF THE EPIPHYSEAL COMPLEX 
 1. The development of the epiphyseal complex in cyclostomes 
 
 According to Studnicka ( ; 93) 384 and other observers, a small 
 evagination in the caudal portion of the roof-plate of the inter- 
 brain makes its appearance as a simple and single protrusion 
 from the roof. This is the pineal organ. There can be no 
 question but that it develops first of the two elements in the 
 epiphyseal complex in these forms. The anlage of the pineal 
 organ increases greatly in size so as to present an end-sac or 
 
40 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 end-vesicle, a stalk and a proximal portion connecting it with a 
 ventricle of the brain. At first, the end-vesicle contains a cavity 
 which gradually decreases in size so that the lumen becomes 
 little more than a cleft or entirely disappears. The stalk also 
 contains a large canal which is gradually reduced in size. The 
 ventral wall of the end-sac becomes converted into a structure 
 resembling the retina, in which many nerve fibers are to be 
 observed. In the dorsal wall of the sac nerve fibers running 
 from the end-vesicle soon make their appearance. These fibers 
 come into relation with the posterior commissure and constitute 
 what is known as the nervus pinealis. The proximal portion is 
 represented by a very short, dilated structure which contains 
 the recessus pinealis. 
 
 Fig. 9 Anlage of the epiphyseal conplex in an embryo of Petromyzon, accord- 
 ing to Kupffer, 1904. 
 
 Ls., lamina terminalis; Pp., paraphysis; Ch., commissura habenularis; Po., 
 pineal organ; Cp., commissura posterior. 
 
 At a considerably later embryonic period the anlage of Stud- 
 nicka's parapineal organ first makes its appearance. It develops 
 entirely independent of the anlage of the pineal organ. The 
 evagination which first makes its appearance as the parapineal 
 anlage shortly becomes greatly elongated to form a tubular 
 prolongation from the roof of the brain. The terminal portion of 
 this tubular evagination becomes dilated to form, as in the case of 
 the pineal organ, an end- vesicle, while a slender stalk connects the 
 latter with the brain roof. The ventral wall of the end-sac of 
 the parapineal organ, as in the case of the pineal organ, develops 
 
THE PINEAL BODY 41 
 
 a pigmented structure and in it appears a number of nerve fibers. 
 In the later embryonic stages the stalk connecting the end- 
 vesicle of the parapineal organ with the brain attenuates, loses 
 its lumen, and shows the presence in it of numerous nerve fibers 
 which may be traced to the commissura habenularis. The rapid 
 elongation of the stalk in the parapineal /and pineal organs as 
 development advances causes these structures to be moved 
 further away from the roof-plate and near the under surface of 
 the skull. The general direction of this growth is cephalodorsad. 
 Gaskell 145 showed in Ammoccetes a right and left pineal eye. 
 It is his opinion that the pineal and parapineal organs represent 
 a paired set of eyes. Their relation to each other, in which the 
 parapineal organ occupies the more cephalic position, was deter- 
 mined, according to Gaskell, by the exigencies of development. 
 In reality, however, he believes that the ancestors of vertebrates 
 must have possessed a pair of median eyes. 
 
 Dendy 86 also observed in cyclostomes a double evagination 
 from the roof-plate giving rise to the epiphyseal complex. It is 
 his opinion that the right evagination produces the parietal eye 
 while the left becomes the parapineal organ, and Dendy, like 
 Gaskell, maintains that the ancestors of the vertebrates must 
 have been possessed of a pair of parietal eyes which may have 
 been serially homologous with the ordinary vertebrate eyes. 
 Scott ('81) 349 and Dohrn (75) 95 both showed that the epiphyseal 
 complex developed as evaginations from the roof of the in- 
 terbrain. These observations were essentially confirmed by 
 Shipley ('87), 354 Owsiannikow ('88), 295 Studnicka ( 7 93), 384 and 
 Kupffer ('94). 224 
 
 2. The development of the epiphyseal complex in selachians 
 
 Balfour 10 in 1878, in Acanthias, d'Erchia 109 in 1896, in Pris- 
 tiurus, and Minot 277 in 1902, also in Pristiurus, investigated the 
 development of the epiphyseal complex. According to all of 
 these authors, a single evagination . arises in the roof -plate im- 
 mediately in front of what is later to be the posterior commissure. 
 This evagination gives rise to the pineal organ inasmuch as the 
 parapineal organ does not appear in selachians. From its 
 
42 FREDERICK TELNET AND LUTHER F. WARREN 
 
 inception this evagination is a small, cordiform enlargement 
 which rests at first directly upon the ectoderm of the upper 
 surface of the head. The gradual lengthening of the tubular 
 pineal organ, which is similar to what occurs in Petromyzon, is 
 in the main due to the fact that a very large amount of mesen- 
 chyme makes its appearance between the roof of the brain and 
 the under surface of the skull. In this way the end-vesicle of 
 the pineal organ maintains its relative position to the ectoderm 
 and thus always remains near the surface of the skin. In many 
 instances the end-vesicle comes to lie in a large foramen of the 
 skull, that is, the parietal foramen which makes its appearance 
 at a later stage of development. 
 
 Considering the embryological development of the pineal 
 region in selachians, Locy 244 holds that two pairs of accessory 
 optic vesicles are preserved in the cephalic plate of Elasmo- 
 branchs, his particular reference being to Squalus acanthias. 
 These accessory optic vesicles together with the primary optic 
 vesicles give rise to two pairs of rudimentary eyes. The epi- 
 physis is, therefore, of double origin, forming a united pair of 
 accessory optic vesicles, and since the latter are homologous 
 with the lateral eyes, the epiphysis itself must be homologous 
 with these eyes also. His contention that the pineal outgrowths 
 arise from two pairs of vesicles that are homologous with those 
 giving origin to the lateral eyes has not been altogether sustained 
 by other observers. Locy is also of the opinion that it is highly 
 probable that the enlarged distal end of the epiphysis in Squalus 
 is homologous with the pineal eye in those forms in which it is 
 differentiated. Goette 152 in 1875 expressed the opinion that the 
 epiphysis in selachians was a product of differentiation at the 
 point of union between the brain and the epidermis. He com- 
 pares the pineal organ to the pore which persists for a long time 
 in the embryo of Amphioxus and leads into the encephalic cavi- 
 ties. Ehlers 108 in 1878 confirmed the findings of Balfour in 
 Raia clavata and Acanthias vulgaris. An interesting observa- 
 tion in this connection is the finding by Cattie 60 of the pineal 
 organ in Torpedo marmorata. Cattie observed the organ in the 
 embryonic state in this form. The importance of this observa- 
 
THE PINEAL BODY 
 
 tion lies in the fact that Studnicka 391 says that the organ is absent 
 in Torpedo marmorata and d'Erchia 109 says that in Torpedo 
 ocellata there is no pineal organ. 
 
 Fig. 10 The epiphyseal complex in an 86 mm. embryo of Acanthias vulgaris, 
 according to Minot, 1901. 
 
 Hm., hemisphere; Pf., paraphysis, V., velum transversum; Ds., dorsal sac: 
 Ch., commissura habenularis; R., recessus pinealis; Po., pineal organ; Cp.,com- 
 missura posterior; M., midbrain. 
 
 One of the authors, Tilney ('15), 396 studying the interbrain in 
 Mustelus laevis, illustrated the development of the pineal organ 
 in reconstruction models through a number of stages. The 
 anlage of the epiphyseal complex in Mustelus makes its first 
 appearance in the 9 mm. embryo as a single evagination from the 
 roof-plate. It is a prominent element in this region for some 
 
44 FKEDERICK TILNEY AND LUTHER F. WARREN 
 
 time before the appearance of the paraphysis. In the embryo 
 of an !! mm. Mustelus the evagination appears rising well 
 above the general plane of the roof. 
 
 It is bounded by a thin cephalic and a thicker caudal wall. 
 A recess of considerable depth extends into it; it retains com- 
 
 44 
 
 29 
 
 Fig. 11 Mesial view of forebrain reconstruction of 11 mm. Mustelus embryo. 
 X 100. The unshaded area shows the cut surfaces of the reconstruction. Ac- 
 cording to Tilney, 1915. 
 
 4, chiasm; 7, epiphysis; 18, infundibular evagination; 24, midbrain; 25, mam- 
 millary region; 29, optic evagination; 36, post-infundibular evagination; 44, tel- 
 encephalon; 45, tuberculum postero-superius; 46, tubercle of the floor of Schulte. 
 
 munication with the third ventricle. The inception of the velum 
 transversum may be discerned, but no paraphysis is present. 
 The changes observed in passing from the 11 mm. to the 20 mm. 
 embryo consist in the now definite appearance of the velum 
 transversum and the elongation of the pineal organ. 
 
THE PINEAL BODY 
 24 
 
 45 
 
 42 
 
 3332 
 
 Fig. 12 Mesial view of forebrain reconstruction of 20 mm. Mustelus. X 75. 
 The unshaded area shows the cut surfaces of the reconstruction. According to 
 Tilney, 1915. 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 18, infundibular 
 evagination; 24, midbrain; 25, mammillary region; 32, post-chiasmatic eminence; 
 33, post-chiasmatic recess; 36, post-infundibular eminence; 41, supra-optic crest; 
 42, supra-optic recess; 44, telencephalon; 45, tuberculum postero-superius ; 46, 
 tubercle of the floor of Schulte; 47, velum transversum. 
 
 In the latter there is a slight tendency for the evagination to 
 become expanded as if to form an end-vesicle. It is, therefore, 
 possible at this time to recognize a stalk and an end-sac. 
 Neither in this stage nor in any subsequent period of develop- 
 ment is there evidence of a parapineal organ. The paraphysis 
 
46 
 
 FREDERICK TILNEY AND LUTHER F, WARREN 
 
 has not yet made its appearance. In the 50 mm. embryo, how- 
 ever, the paraphyseal anlage is present and the pineal organ 
 has become still further elongated. 
 
 The tendency toward expansion of the dista 1 extremity is not 
 as marked as in the 20 mm. embryo. The pineal organ still 
 contains a lumen throughout its entire extent. The expansion 
 of the pineal organ to form an end-sac is again pronounced at 
 the stage of 70 mm. 
 
 44 
 
 39 
 
 32 
 
 13 
 
 Fig. 13 Mesial view of forebrain reconstruction of 50 mm. Mustelus. X 50. 
 The unshaded area shows the cut surfaces of the reconstruction. According to 
 Tilney, 1915. 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 13, infundibular 
 process; 24, midbrain; 25, mammillary region; 32, post-chiasmatic eminence 
 (lobus-inf erior) ; 33, post-chiasmatic recess (recess of inferior lobe); 36, post- 
 infundibular evagination; 39, paraphysis; 40, recess of infundibular process; 41, 
 supra-optic crest ; 42, supra-optic recess ; 44, telencephalon ; 47, velum transversum . 
 
THE PINEAL BODY 
 
 47 
 
 The sac is hollow and in communication with the ventricle by 
 means of a slender, hollow stalk. A proximal portion may now 
 be distinguished so that all three elements of the pineal organ are 
 present. The habenular ganglion is recognizable at this stage 
 as a marked thickening in the roof-plate cephalad of the pineal 
 organ. The paraphysis and velum have increased in promi- 
 
 24 
 
 42 
 
 Fig. 14 Mesial view of forebrain reconstruction of 70 mm. Mustelus. X 50. 
 The unshaded area shows the cut surfaces of the reconstruction. According to 
 Tilney, 1915 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 18, infundibular 
 evagination; 24, midbrain; 26, mammillary recess; 27, mammillary body (poste- 
 rior lobe) ; 32, post-chiasmatic eminence (inferior lobe) ; 33, post-chiasmatic 
 recess (recess of inferior lobe) : 35, post-infundibular recess; 36, post-infundibular 
 eminence; 39. paraphysis; 40, recess of infundibular process; 41, supra-optic crest; 
 42, supra-optic recess; 44, telencephalon; 47, velum transversum. 
 
 nence. The brains of the 100 mm. and 300 mm. Mustelus 
 approximate the adult conditions shown in figures 15, 16 and 17. 
 Here, with one exception, i.e., the parapineal organ, all of the 
 elements in the pineal region may be identified, including the 
 two parts of the paraphyseal arch, the velum transversum, a 
 short dorsal sac, a massive habenular commissure and habenular 
 
48 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 ganglion, a pineal organ consisting of an end-vesicle, stalk and 
 proximal portion, and finally the posterior commissure. 
 
 39 
 
 Fig. 15 Mesial view of brain reconstruction of 100 mm. Mustelus. X 25. 
 The unshaded area shows the cut surfaces of the reconstruction. According 
 to Tilney, 1915. 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 13, infundibular 
 process; 14, infundibular process, saccular surface; 15, infundibular process, pitui- 
 tary surface; 20, lamina terminalis; 24, midbrain; 27, mammillary body (post- 
 erior lobe) ; 32, post-chiasmatic eminence (lobus inferior) ; 33, post-chiasmatic 
 recess (recess of inferior lobe); 36, post-infundibular evagination; 39, paraphysis; 
 40, recess of infundibular process; 41, supra-optic crest; 42, supra-optic recess; 
 44, telencephalon; 47, velum transversum. 
 
 3. The development of the epiphyseal complex in ganoids 
 
 Kupffer 223 1893 gave the first detailed description of the develop- 
 ment of the epiphyseal complex in Acipenser. The anlage of the 
 organ he describes as a small single evagination which later 
 becomes a stalk with an end-vesicle. Kupffer could find 
 nothing of the anterior or parapineal organ. Owsiannikow 
 ( J 88) 295 gave a description according to which in the three- or 
 four- weeks old embryo of Acipenser just in front of the pineal 
 organ there appears a small, round or cordiform structure.. 
 Hill 180 in 1894 described a small rudiment of the anterior or 
 parapineal organ in Amia calva. In the 10 mm. embryo this 
 body was ovoid in form and situated immediately in front and 
 
THE PINEAL BODY 49 
 
 to the left of the pineal organ. It was connected with the roof- 
 plate by means of a thin stalk. In the 13 mm. embryo this 
 organ has come to lie above the commissura habenularis and 
 still later it is consolidated into a mass of cells lying to the left 
 beneath the now markedly developed and ventrally flexed 
 pineal organ. Eycleshymer and Davis 113 in 1897 confirmed the 
 observation of Hill and noted that the anterior or parapineal 
 
 44 
 
 15 10 
 
 32 33 
 
 Fig. 16 Mesial view of brain reconstruction of 300 mm. Mustelus. X 25. 
 The unshaded area shows the cut surfaces of the reconstruction. According to 
 Tilney, 1915. 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 10, hypophyseal 
 recess; 13, infundibular process; 14, infundibular process, saccular surface; 15, 
 infundibular process, pituitary surface; 24, midbrain; 27, mammillary body (pos- 
 terior lobe); 32, post-chiasmatic eminence (inferior lobe); 33, post-chiasmatic 
 recess (recess of inferior lobe); 36, post-infundibular evagination; 39, paraphysis; 
 40, recess of the infundibular process; 41, supra-optic crest; 42, supra-optic re- 
 cess; 44, telencephalon; 47. velum transversum. 
 
 organ possessed a lumen late in the course of development. 
 Both the anterior and posterior pineal organs in the embryonic 
 stages have nerve fibers which connect them with the habenular 
 commissure. The earlier works upon this region in ganoids were 
 done by Salensky 341 in 1881 and Balfour and Parker 12 in 1882 
 (% 18). 
 
 MEMOIR NO. 9 
 
50 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 4. The development of the epiphyseal complex in teleosts 
 
 Rabl-Rtickhard 318 in 1882 gave the first explanation of the 
 development of the epiphyseal complex in teleosts. Hoffmann 185 
 in 1884 also described the ontogenesis of the pineal organ in 
 
 14 
 
 33 
 
 21 
 
 Fig. 17 Mesial view of brain reconstruction in adult Mustelus laevis. X 25. 
 The unshaded area shows the cut surfaces of the reconstruction. According to 
 Tilney, 1915. 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 6, diverticular sacci vasculosi; 
 7, epiphysis; 10, hypophyseal recess; 12, infundibular canal; 14, infundibular proc- 
 ess, saccular surface; 15, infundibular process, pituitary surface; 20, lamina ter- 
 minalis; 21, median chiasmatic groove; 24, midbrain; 26, mammillary recess (re- 
 cess of posterior lobe) ; 27, mammillary body (posterior lobe) ; 32, post-chiasmatic 
 eminence (inferior lobe) ; 33, post-chiasmatic recess (recess of inferior lobe) ; 34, 
 post-infundibular eminence; 35, post-infundibular recess; 39, paraphysis; 42, 
 supra-optic recess; 44, telencephalon; 47, velum transversum. 
 
 teleosts. Both authors employed the same forms, namely, 
 Salmo fario and Salmo solar. According to their descriptions, 
 the anlage begins as a small evagination which gradually elon- 
 gates and grows more and more narrow. It has produced a 
 proximal portion, a stalk and an end- vesicle which lie just 
 beneath the inner surface of the skull in the frontal region. 
 
THE PINEAL BODY 
 
 51 
 
 Still later many small diverticula develop in the walls of the 
 end-vesicle which become unusually large. A feature of the 
 description of the development given by these authors is the 
 absence of any anterior or parapineal element in the epiphyseal 
 complex, for this organ, according to their observations, does 
 
 M 
 
 Cp R Ch Ds V Pf 
 
 Rn 
 
 Fig. 18 The epiphyseal complex in a four months old embryo of Acipenser 
 sturio, according to Kupffer, 1893. 
 
 Ls., lamina terminalis; Pf., paraphysis; V., velum trans versum; Ds., dorsal 
 sac; Ch., commissura habenularis; R., recessus pinealis and pineal organ; Cp., 
 commissura posterior; M., midbrain. 
 
 not even make its appearance in anlage. Holt ('91) 189 described 
 the development of the epiphyseal complex in Clupea harengus. 
 In this form the organ began as a solid sprout and later devel- 
 oped a lumen. The walls of the end- vesicle were eventually 
 thrown into a number of diverticula. Mclntosh and Prince 254 
 in 1891 confirmed the findings of Hoffmann and Rabl-Ruckhard. 
 Hill's 179 observation in 1891 is of unusual importance, for this 
 observer, working upon Coregonus albus and later 180 in 1894 on 
 Salmo catostomus teres, Stizosthetium vitreum, and Liponus 
 callidus, found what he took to be the anlage of the anterior or 
 parapineal element just as he had found this element in Amia 
 
52 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 calva. In the embryo of Salmo fontinalis , Hill 180 found the 
 anlage of the epiphyseal complex to be a double evagination 
 which communicated with the third ventricle by means of a 
 common canal. Of the two sacs thus formed the posterior was 
 much the larger. This, the anlage of the pineal organ, was 
 situated immediately in front of the posterior commissure and 
 in the mid-line, while the anterior evagination was close to the 
 left as if both sacs were related to the roof-plate by a common 
 stalk and later the anterior one was detached from the connec- 
 tion. Hill concluded that there are two epiphyseal outgrowths 
 from the roof in teleosts of which the more anterior vesicle, both 
 in teleosts and in Amia, is homologous with the parietal eye of 
 
 Po 
 
 Pp 
 
 Fig. 19 Anlage of the epiphyseal complex in a 37.-days old embryo of Salmo 
 fontinalis, according to Hill, 1894. 
 
 Pp., parapineal organ; Po., pineal organ. 
 
 Lacertilia. He thinks it probable that the two vesicles in their 
 primitive position were side by side and believes it likely that 
 the anterior vesicle is the homologue of the parapineal organ in 
 Petromyzon. Hill also found this condition in embryos as well 
 as in a two-year-old salmon. 
 
 Dendy 86 maintained that the double evagination in the epi- 
 physeal anlage occurs in Amia as well as leleosts. Of these two 
 vesicles the right gives rise to the epiphysis while the left sepa- 
 rates from the brain and degenerates. Cattie, 60 examining the 
 adult condition in plagiostomes, ganoids, and teleosts, came to a 
 conclusion similar to the hypotheses of Goette 152 and Van Wijhe 407 
 that the pineal body was derived as the final product of closure 
 at the anterior neuropore where the ectoderm of the epidermis 
 
THE PINEAL BODY 53 
 
 and of the nerve tube remained longest in continuity. Van 
 Wijhe 407 in 1884 expressed the belief that the epiphysis in teleosts 
 was a remnant of the anterior neuropore, but later he gave up 
 this idea. Rabl-Riickhard 318 in 1882, studying the epiphysis in 
 embryos of bony fish, summarized the process of development 
 from the comparative standpoint in the following words: 
 
 Allein wahrend diese unter Mitwirkung des sich zur Linse einstul- 
 penden Ectoderms und des Mesoderms complicirte Veranderungen ein- 
 gehen, die schliesslich zur Entwickelung des hochst entwickelten Sin- 
 nesorganes, des Auges, fiihren, sehen wier an der Zirbeldriise trotz der 
 giinstigen Lage ihres distalen Endes dicht unter dem Ectoderm nichts 
 dergleichen. Mann denke sich eine ahnliche Wucherung und ihre Folgen, 
 wie an dem die Augenblasen bedeckenden Ectoderm, das Auftreten von 
 Pigment im sich betheiligenden Mesoderm, und nichts steht der Vor- 
 stellung im Wege, dass sich aus der Zirbel ein dem Auge dhnliches, un- 
 paares Sinnesorgan entwickelt. Interessant ist, dass diese Gegend in 
 einem bestimmten Embryonal-stadium bei Reptilien (Lacerta Anguis) 
 eine ahnliche Entwickelung wenigstens andeutungsweise zeigt, und dass 
 hier am Scheitelbeine des fertigen Thieres sich ein Kreisrundes Loch 
 befindet. Bekanntlich hat schon Ley dig diesen Befund eingehend 
 erortert und die Vermuthung ausgesprochen, dass es sich vielleicht um 
 ein "Organ des 6 Shines" handelt. 
 
 And again in 1886: 
 
 Das. Schadeldach der riesigen fossilen Enaliosaurier des Lais des Ich- 
 thyosaurus und Plesiosaurus besitzt ein unpaares Loch, welches seiner 
 Lage nach mit dem Loch in Scheitelbein der Saurier ubereinzustimmen 
 scheint. Vielleicht lag auch hier das viel entwickeltere Zirbelorgan 
 mit seinem distalen Endtheil zu Tage, und man konnte sich vorstellen 
 das seine Leistung nicht sowohl die eines Sehorgan als die eines Organs 
 des Warmesinnes war, dazu bestimmt, seine Trager vor der zu inten- 
 siven Einwirkung der trophischen Sonnenstrahlen zu warnen, wenn sie 
 in trager Ruh, nach Art ihrer noch lebenden Vettern der Crocodile, 
 sich am Strande und auf den Sandbanken der Laisse sonnten. 
 
 5. The development of the epiphyseal complex in amphibia 
 
 In Urodela, deGraaf ('86) 155 found that the embryo of Triton 
 had the anlage of its epiphyseal complex in a simple and single 
 saccular evagination from the roof of the interbrain. These 
 observations were confirmed upion Amblyswma embryos by 
 Orr 286 in 1899, by His 183 in 1892 and by Eycleshymer 112 in 1892. 
 Beraneck 24 in 1893, working upon Salamandra embryos, observed 
 
54 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 the anlage of the epiphyseal complex to be a hollow sac which 
 later became saccular and cylindrical, containing throughout its 
 entire extent a lumen which still opened into the third ventricle. 
 In this form it was possible to identify an end- vesicle, a stalk, and 
 a proximal portion. These conditions were obtained at a period 
 of 12 mm. embryo, but at the stage of the 18-mm. embryo the 
 lumen in the stalk was obliterated. In this manner the stalk of 
 the pineal organ became gradually reduced in size until finally 
 it presented itself as a mere strand connecting an almost com- 
 pletely isolated end-vesicle lying beneath the skull with a well- 
 marked proximal portion in communication with the third 
 ventricle. In Salamandra the paraphysis develops very early 
 and assumes extensive proportions resembling the chorioid 
 plexus. The embryological conditions in Anura are, according 
 to most descriptions, quite similar to those in Urodela. Goette 152 
 in 1873-75 observed in the anlage of the pineal organ the remains 
 of the anterior neuropore. This error, as has already been 
 stated, was pointed out by Hoffmann 186 in 1886 and Heckscher 1690 
 in 1890. In Rana, Beraneck 24 described the first appearance of 
 the anlage of the epiphyseal complex as a small, ellipsoid evagi- 
 nation which later becomes cylindrical. This evagination con- 
 tains a small lumen. Elongation gradually occurs so that an 
 end- vesicle, a stalk, and a proximal portion are formed. In the 
 later stages of development the stalk undergoes attenuation 
 until it is reduced to a mere strand containing, it is thought, 
 some nerve fibers. This leaves the end-vesicle situated at a 
 point remote from the brain beneath the skull, while the proximal 
 portion is a large and somewhat spacious evagination still main- 
 taining a wide connection with the third ventricle. The nearly 
 isolated end- vesicle Beraneck calls the corpus epitheliale. This 
 body lies beneath the skin over the head and has the appearance 
 of a gland-like structure. In embryos of Bufo, Beraneck 24 
 observed close to the commissura habenularis a small prominence 
 which early disappears; this he identified as the anlage of a 
 transitory parapineal organ. For the most part, however, 
 observers have found that a single evagination in the roof-plate 
 marks the anlage of the epiphyseal complex (fig. 20). 
 
THE PINEAL BODY 55 
 
 Eycleshymer, 112 in attempting to explain the unpaired origin 
 of the epiphysis in Amblystoma, maintained that in the phylo- 
 genetic period when the lateral eyes became implicated by the 
 closing of the neural fold, a median eye would arise and thus 
 become most highly functional during the time when the lateral 
 eyes were little, if at all, functional. Cameron, 50 working with 
 the embryos of Rana, Bufo, and Triton, concluded that the 
 
 Fig. 20 Anlage of the epiphyseal complex in a 13 mm. embryo of Salamandra 
 maculata, according to Kupffer, 1893. 
 
 Ls., lamina terminalis; Pf., paraphysis; V., velum transversum; Ds., dorsal 
 sac; Ch., commissura habenularis; Po., pineal organ; Sch., pars intercalaris pos- 
 terior; Cp., commissura posterior; M, midbrain. 
 
 epiphysis in amphibia arises as two primary outgrowths from 
 the roof of the forebrain (fig. 21). 
 
 These are placed one on either side of the mesial plane. The 
 outgrowth situated to the right of the middle line disappears at 
 an early age by blending with the left outgrowth. The latter 
 shows most active growth so that the epiphyseal opening becomes 
 situated to the left of the mesial plane. The left outgrowth, 
 
56 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 however, is the more important of the two in amphibia. Cam- 
 eron believes that there is evidence of a bilateral origin to be 
 found in the later stages of amphibian development. The 
 portion of the anlage in connection with the superior commissure 
 corresponds to the parietal eye of Sphenodon while the remainder 
 corresponds to the epiphyseal stalk. From this evidence in 
 amphibia he is inclined to agree with Dendy 86 that the ancestors 
 of vertebrates must have possessed a pair of parietal eyes (figs. 
 22 and 23). 
 
 
 Fig. 21 Anlage of the epiphyseal complex in an embryo of Triton cristatus, 
 according to deGraaf, 1886. 
 
 Ch., commissura habenularis; R., recessus and pineal organ; Cp., commissura 
 posterior; M., midbrain; Epid., epidermis; Cor., corium. 
 
 6. The development of the epiphyseal complex in reptilia 
 
 The fact that in Prosaurians and Saurians a well developed 
 ye is found in many forms has been the cause of much dis- 
 cussion as to the embryolgical process by means of which this 
 structure is differentiated from the epiphyseal complex. Accord- 
 ing to the older view, the parietal eye arose, as in the case of the 
 isolated end-vesicle of amphibia, by a process of constriction 
 from the terminal portion of the pineal organ. Subsequently 
 the view was advanced that instead of a process of constriction 
 
THE PINEAL BODY 
 
 57 
 
 it was rather a subdivision of a single evagination from the roof- 
 plate which gave rise to the parietal eye; more recently, however, 
 the opinion has been expressed by several observers, that the 
 parietal eye owes its existence to an anlage quite independent 
 from that of the pineal organ and situated anterior to the latter 
 in its point of development from the roof-plate of the inter- 
 brain. The fact that the parietal eye was not the constricted 
 end of the epiphysis, but was independently connected by 
 
 Fig. 22 Anlage of the epiphyseal complex in an 11 mm larva of Bufo vulgaris 
 according to Beraneck, 1893. 
 
 Po., pineal organ (end-vesicle); Ep., proximal portion. 
 
 means of a nerve of its own to the roof of the brain, was shown 
 conclusively by Strahl and Martin 383 as well as Beraneck, 23 who 
 was first to call attention to the nerve fibers connecting the 
 parietal eye with the brain, namely, the parietal nerve. Having 
 thus dispensed with the idea that the parietal eye was merely a 
 constricted portion of the end of the epiphysis proper, it re- 
 mained for subsequent investigation to demonstrate the actual 
 process by means of which the parietal eye arose. Advocating 
 the view that the anlage of the epiphyseal complex in Reptilia, 
 and particularly in the Saurian and Prosaurian forms, is an 
 evagination subdivided into an anterior and a posterior compart- 
 
58 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 ment, there has been assembled a formidable array of evidence* 
 Hoffmann/ 86 from his observations on Lacerta agilis, Strahl and 
 Martin, 383 in Anguis and Lacerta vivipara, Francotte, 127 on 
 Lacerta vivipara, Klinckowstroem, 207 in Iguana, McKay, 255 in 
 Grammatophora muricata, and Schauinsland, 346 in Sphenodon 
 all advocate this view (fig. 24). 
 
 Fig. 23 Anlage of the epiphyseal complex in a 12mm. larva of Buf o vulgaris 
 according to Beraneck, 1893. 
 
 Po., pineal organ; Ep., proximal portion. 
 
 Beraneck, 23 on the other hand, in his well-known work upon 
 the parietal eye and the morphology of the third eye of verte- 
 brates, concludes that the parietal eye should not be considered 
 as a simple diverticulum of the pineal gland. In Lacerta and 
 Anguis it constitutes an independent organ which develops from 
 the thalamencephalon as the epiphysis, but develops parallel to 
 the latter not dependent upon it. The parietal eye is attached 
 by a neural fasciculus which is transitory and not in any sense 
 derived from the epiphysis (fig. 25). 
 
THE PINEAL BODY 59 
 
 It is part of the small mass of cells situated between the base 
 of the pineal gland and the first fold of the chorioid plexus. The 
 unpaired eye is an evagination of the dorsal wall of the inter- 
 brain and constitutes, an optic vesicle. The separation which 
 sometimes occurs between the crystalline and retina of this 
 vesicle is ordinarily unilateral, rarely bilateral. It appears 
 relatively late in embryonic development and should not be con- 
 sidered a proof of the duality of origin of the parietal organ as 
 Beard 18 has considered it. The unpaired eye does not occur in 
 chordates nor does it have its homologue in the other branches 
 of the metazoa. Sometimes it has its physiological analogue in 
 the median eye of Crustaceans. It is an ancestral organ which 
 was atrophied in the majority of extant forms of the different 
 
 Fig. 24 Two successive stages in the development of the epiphyseal complex 
 in Lacerta vivipara, according to Francotte, 1896. 
 
 Pa., parapineal organ; Po., pineal organ; M., midbrain. 
 
 branches of the chordate phylum. The primitive optic vesicle is 
 still recognizable in cyclostomes and Saurians; it is rudimentary 
 in teleosts and amphibians, but appears to be absent in sela- 
 chians. On the other hand, the epiphysis in these latter forms 
 is very long and broadened at its distal extremity without form- 
 ing an optic vesicle. The epiphysis is also derived from an 
 evagination of the interbrain roof. It does not represent the 
 optic pedicle of the parietal eye. It is an organ sui generis 
 whose function is still unknown. It reveals no marked sensory 
 characteristics even in selachians where it is markedly .devel- 
 oped. It appears in the entire series of vertebrates and is an 
 ancestral organ. The paired eye and epiphysis appertain to the 
 interbrain while the paraphysis is part of the endbrain. This 
 
60 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 paraphysis shows no features of sensory function. Of these 
 three encephalic diverticula from the roof-plate in Saurians, 
 the parietal eye alone seems to have had ancestral sensory 
 function (fig. 26). 
 
 In a later communication, combating the contention of Klinck- 
 owstroem 207 to the effect that the evolutional process observed 
 in Anguis is normal and more primitive while that in Lacerta 
 is a simple modification of this . primitive form, Beraneck 25 pro- 
 
 Fig. 
 
 The epiphyseal complex in a 27 mm. embryo of Anguis fragilis, ac- 
 
 cording to Beraneck, 1892. 
 
 Pf., paraphysis; V., velum transversum; Ds., dorsal sac; Ch., commissura ha- 
 benularis; Npar., nervus parapinealis; Pa., parapineal organ; Ep., pineal organ; 
 Sch., pars intercalaris posterior; Cp., commissura posterior. 
 
 posed this question, "If in Anguis the parietal eye is only a 
 differentiation of the distal extremity of the epiphysis, how in 
 Lacena does this visual organ develop parallel to the epiphysis 
 and not dependent upon it?" Beraneck maintains that Klinc- 
 kowstroem escapes the difficulty proposed by this question in 
 claiming that the pineal eye of Iguana and Lacerta upon the 
 one hand and Anguis upon the other take origin from different 
 parts of the epiphyseal evagination. Beraneck formulates the 
 hypothesis that the parietal eye and epiphysis represent in 
 
THE PINEAL BODY 
 
 61 
 
 Lacerta two distinct evaginations of the thalamencephalic roof. 
 If they appear to be different in Iguana and Anguis that is due to 
 secondary modifications of this region. The evolution of the 
 parietal eye in Iguana is intermediate between the conditions 
 observed in Lacerta and Anguis. In his conclusion, Beraneck 
 emphasizes his belief that the embryonic facts contradict the 
 
 
 Ch 
 
 Fig. 26 Frontal section showing epiphyseal complex in a 26-day old Iguana 
 tuberculata, according to Klinckowstroem, 1894. 
 
 P/., paraphysis; Ds., dorsal sac; Npar., nervus parapinealis; Ep., proximal 
 portion of pineal organ; Ch , commissura habenularis; Af., midbrain 
 
 epiphyseal origin of the parietal eye in Saurians and confirm 
 the hypothesis of its embryonic individuality. Leydig 238 in 
 1891 confirmed the view of Beraneck in Lacerta agilis. Bendy 86 
 also states that the parietal eye and what he calls the parietal 
 stalk arise from two distinct evaginations in the roof-plate of 
 the interbrain. By parietal stalk, Bendy refers to the portion 
 of the epiphyseal complex here referred to as the pineal organ. 
 
7 /W / *y /^t 
 
 </.% / fiO 
 
 / ' i i 
 
 M 
 
 SchJ 
 
 M 
 
THE PINEAL BODY 
 
 63 
 
 The development of the epiphyseal complex in Ophidia, Chelonia, 
 and Crocodilia. The embryonic description which holds good 
 for the more primitive forms of reptiles must be much modified 
 in dealing with the more highly organized and modern forms of 
 this class. Hoffmann 186 showed that in these reptiles the anlage 
 of the epiphyseal complex is laid down as a single evagination 
 
 AT. , . 
 
 Fig. 29 The epiphyseal complex in Tropidonotus natrix, according to Stud- 
 nicka, 1893. 
 
 Pf., paraphysis; Ds., dorsal sac; Ch.. commissura habenularis; Ep., proximal 
 portion of pineal organ; R., recessus pinealis. Cp., commissura posterior; M., 
 midbrain. 
 
 from the roof-plate immediately anterior to the posterior com- 
 missure. This hollow evagination is ultimately transformed 
 into a solid body. Such a transformation has been shown by 
 Ley dig 210 and Studnicka 389 in Tropidonotus (figs. 29 and 30). 
 
 Fig. 27 The epiphyseal complex in a 31 mm. embryo of Gehyra oceanica, ac- 
 cording to Stemmler, 1900. 
 
 Pf., paraphysis; V., velum transversum; Ds., dorsal sac; Ch., commissura 
 habenularis; Ep., pineal organ; Cp., posterior commissure; M., midbrain. 
 
 Fig. 28 The epiphyseal complex in a 33 mm . embryo of Platydactylus muralis, 
 according to Melchers, 1899. 
 
 Pf., paraphysis; Ds., dorsal sac; Ch., commissura habenularis; Ep., pmea 
 organ; Sch., pars intercalaris posterior; M, midbrain. 
 
64 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 The cells constituting this solid organ arrange themselves 
 more or less in alveolar or aciniform cell groups and the whole 
 body ultimately becomes attached to the roof -plate by means of 
 a thin stalk or peduncle. No evidence of an anterior evagina- 
 tion representing the parapineal element has been observed nor 
 is there any evidence to show that any effort toward the devel- 
 opment of the parietal eye in Ophidia, Chelonia, or Crocodilia 
 
 Fig. 30 The epiphyseal complex in an older Tropidonotus embryo, according 
 to Leydig, 1897. 
 
 P/., Paraphysis; Ds., dorsal sac; Ch., commissura habemilaris; Ep., proximal 
 portion of pineal gland. 
 
 is present. In fact, in the latter forms, namely, Crocodilia, the 
 entire epiphyseal complex is said to be wanting and no evidence 
 of its development occurs at any time during ontogenesis (figs. 
 31 and 32). 
 
 One of the authors, studying the development of the epiphysis 
 in turtles, reconstructed the forebrain of Thalassochelys caretia 
 in several stages. The conditions in the 30 mm. embryo are 
 shown in figure 33. Here the pineal region consists of a well- 
 
(./ 
 
 Hm 
 
 M 
 
 Fig. 31 The epiphyseal complex in an old embryo of Chelydra serpentina, 
 according to Humphrey, 1894. 
 
 Pf., paraphysis; V., velum transversum; Ds., dorsal sac; Ep., pineal organ; Cp., 
 posterior commissure. 
 
 Fig. 32 The pineal region in an old embryo of Caiman niger, according to 
 Voeltzkow, 1903. 
 
 Hm., hemisphere; Pf., paraphysis; Ds., dorsal sac; Ch., commissura habenu- 
 laris; Af, midbrain. 
 
 65 
 
 MEMOIR NO. 9 
 
66 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 marked paraphyseal evagination, a velum transversum, a dorsal 
 sac, a commissura habenularis, and a single thick-walled anlage of 
 the pineal body whose apex is directed cephalad. The most 
 caudal structure in the pineal region is the posterior commissure. 
 
 Pf 
 
 Fig. 33 Reconstruction of a 30 mm. embryo of Thalassochelys caretta. 
 
 Ls., lamina terminalis; Pf., paraphysis; V., velum transversum; Ds., dorsal 
 sac; Ch., commissura habenularis; Po., epiphysis; Cp., posterior commissure; R., 
 Rathke pocket. 
 
THE PINEAL BODY 
 
 67 
 
 7. The development of the epiphyseal complex in aves 
 
 In birds, the anlage of the epiphyseal complex makes its first 
 appearance as a simple and single evagination. This was first 
 observed and described by Reissner 329 in 1851 and called by 
 Reichert 326 in 1859 the recessus pinealis. Lieberktihn 242 in 1871 
 identified this evagination in birds as the anlage of the epiphysis. 
 
 In many instances the presence of a double evagination of 
 the roof-plate has been reported in the anlage of the epiphysis 
 in birds. Saint Remy 340 in 1897 found on either side of the still 
 unclosed neural tube a small evagination in the region of the 
 
 Fig. 34 The epiphyseal complex in an 8-day embryo of Anas domesticata, 
 according to Hechscher, 1890. 
 
 epiphyseal anlage. This observation was made upon Gallus, 
 but Parker 301 in 1892, in Apieryx, and Klinckowstroem 206 in 
 1892, in Larus, mentioned an evagination in front of the epi- 
 physeal anlage. Hill 181 in 1900 observed in a closed neural tube 
 two such evaginations. Whether it is justified to consider the 
 anlage of the epiphysis in birds as bilateral or double or whether 
 one of these evaginations represent the remnant of the para- 
 pineal organ, is a difficult question to decide. By many these 
 reduplications in the anlage are considered as pathological since 
 they occur only in isolated instances of the several species 
 described. The most common form in which the anlage in birds 
 
68 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 presents itself is a single evagination in front of the posterior 
 commissure. The further differentiation of the epiphysis is 
 given by Lieberkiihn 242 in Gallus and also in much more detail by 
 Mihalkovicz 274 in 1874 and 1877. According to the description 
 of the latter, the principal change from the original saccular 
 evagination in the roof-plate consists in the conversion of the 
 original sac into a folliculated structure which presents many 
 alveoliform cell groups as a result of the rapid proliferation in 
 the walls of the original saccular anlage. Henrichs ('96) 173 
 found that the follicles first developed as hollow buds in com- 
 munication with the main cavity of the original epiphyseal 
 anlage, Later these buds become branched and in this way a 
 rich follicular system is developed. 
 
 Fig. 35 The epiphyseal complex in an embryo of Sterna hirundo. according to 
 Klinckowstroem,"1891. 
 
 According to Henrichs, the paraphysis first appears as a solid 
 sprout and later acquires a lumen. Cameron 51 showed in the 
 chick that the epiphyseal anlage is a double outgrowth, the left 
 being the larger. These two evaginations ultimately coalesce. 
 Practically the same condition is observed in amphibia. Gar- 
 jano 144 makes the observation which in the main covers the con- 
 ditions observed in birds, namely, that as compared with the 
 lower vertebrates the pineal body is a profoundly altered organ 
 in birds and mammals. 
 
 One of the authors in a recent work on the diencephalon re- 
 produces illustrations of reconstruction models which show the 
 development in the pineal region of Gallus gallus. The first 
 
THE PINEAL BODY 
 
 69 
 
 evidence of the epiphyseal complex in the chick makes its appear- 
 ance at five days and twenty hours as a sprout from the caudal 
 extremity of the interbrain roof-plate. This sprout contains a 
 narrow canal and at this very early period shows an apparent 
 differentiation into an expanded distal portion, a stalk, and an 
 expanded proximal portion. 
 
 Fig. 36 Mesial view of forebrain reconstruction of chick of 5 days and 20 
 hours. X 100. The unshaded area shows the cut surfaces of the reconstruction, 
 according to Tilney, 1915. 
 
 2, chiasmatic process; 4, chiasm; 7, epiphysis; 13, infundibular process; 20, 
 lamina terminalis; 25, mamrnillary region; 32, post-chiasmatic eminence; 33, post- 
 chiasmatic recess; 36, post-infundibular eminence; 38, pre-optic recess; 39, para- 
 physis; 41, supra-optic crest; 42, supra-optic recess; 44, telencephalon; 45, tuber- 
 culum postero-superius; 46, tubercle of the floor of Schulte. 
 
70 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 At this time the pineal region presents a well-marked para- 
 physis, a velum transversum, and a dorsal sac. At the stage of 
 eight days in the chick a marked change is noticed, for at this 
 period of development the pineal anlage has the appearance of a 
 wide and expansive evagination in free communication with the 
 third ventricle. 
 
 Fig 37 Mesial view of forebrain reconstruction of chick of 8 days X 50. 
 The unshaded area shows the cut surfaces of the reconstruction, according to 
 Tilney, 1915. 
 
 2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 9, foramen of 
 Monro; 11, infundibular stem; 12, infundibular canal; 13, infundibular process; 
 24, midbrain; 25, mammillary region; 26, mammillary recess; 32, post-chiasmatic 
 eminence; 35, post-infundibular recess; 36, post-infundibular eminence; 38, pre- 
 chiasmatic recess; 39, paraphysis; 41, supra-optic crest; 42, supra-optic recess; 
 44, telencephalon. 
 
 The brain of the chick at fourteen days and eighteen hours 
 shows a marked alteration in the pineal region, as a result of 
 which the development of the epiphysis seems to overshadow all 
 other structures in this region. The walls of the evagination 
 which characterize the pineal organ in the eight-day chick have 
 become greatly thickened near the distal extremity of the epi- 
 physis so that now this portion of the organ is practically solid 
 
THE PINEAL BODY 
 
 71 
 
 with the exception of a very small lumen which extends almost 
 throughout its entire extent. A very large pineal recess is 
 present. The dorsal sac and paraphysis are both much reduced 
 in size. There is no evidence of any distal portion of the pineal 
 organ at this period. No sign of an evagination or anlage which 
 might be interpreted as the parapineal organ was found in this 
 study. 
 
 39 
 
 Fig. 38 Mesial view of forebrain reconstruction of 14 days and 18 hours chick. 
 X 25, according to Tilney, 1915. 
 
 1, aqueduct of Sylvius; 2, chiasmatic process; 3, cerebellum; 4, optic chiasm; 7, 
 epiphysis; 9, foramen of Monro; 12, infundibular canal; 14, infundibular process, 
 saccular surface; 15, infundibular process, pituitary surface; 24, midbrain; 26, 
 mammillary recess; 27, mammillary body; 32, post-chiasmatic eminence; 33, post- 
 chiasmatic recess; 36, post-infundibular eminence; 38, pre-chiasmatic recess; 39, 
 paraphysis; 41, supra-optic crest; 42, supra-optic recess; 44, telencephalon. 
 
72 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 8. The development of the epiphyseal complex in mammals 
 
 The only portion of the epiphyseal complex which appears in 
 the anlr,ge in mammals is, in all probability, the proximal part 
 of the pineal organ, for there is no evidence of the anterior or 
 parapineal element. Mihalkovicz 275 in 1877 gave a description 
 of the development of the organ in mammals and called attention 
 to the fact that it resembled very closely that of birds. At first 
 the anlage is a simple evagination, then several lateral diverticula 
 about the same size make their appearance and later give rise to 
 many follicles. The lumen of each follicle from the beginning is 
 smaller than that in birds and ultimately is obliterated so that 
 there are finally solid follicles surrounded by connective tissue 
 and blood vessels. The epiphysis always retains its connection 
 with the interbrain by means of a set of peduncles. These 
 peduncles vary in their arrangement and number according to 
 the form of the animal. In man they are described by Testut 393 
 as being three pairs, known respectively as the superior, middle, 
 and inferior peduncles of the pineal body. Mihalkovicz gave 
 his description of the relations of the anlage to the roof-plate as 
 he observed them particularly in the rabbit. 
 
 Kraushaar 221 in 1885 confirmed these findings in the mouse 
 and Kolliker 211 in 1879 in the rabbit and 'sheep. d'Erchia 109 in 
 1896 found that the epiphysis in the guinea-pig is laid down as 
 a solid bud or sprout, while in man it has in its anlage a small 
 lumen from the beginning (fig. 39). 
 
 Neumeyer 282 in 1899 found in the rabbit that the epiphyseal 
 anlage was a long, tubular structure with a narrow lumen and 
 considerably convoluted. The original lumen of the anlage is 
 ultimately reduced until it occupies the proximal portion only 
 where it is known as the recessus pinealis, according to Reichert, 326 
 or the recessus infrapinealis, according to Mihalkovicz. 275 This 
 distinction takes account of the description already given by 
 Reichert of the suprapineal recess. 
 
 In studying the development of the diencephalon in the 
 domestic cat one of the authors illustrates by reconstruction 
 models of the following embryos: In Felis domeslica, the pineal 
 
THE PINEAL BODY 
 
 73 
 
 organ shows the first appearance of the epiphyseal complex at 
 the stage of 30 mm. embryo where it takes the form of a wide, 
 single evagination immediately cephalad to the posterior com- 
 missure. This evagination contains a recess in free communica- 
 tion with the third ventricle (fig. 40). 
 
 In a cat embryo of 51 mm. a notable change has taken place 
 in the epiphyseal anlage shown in the fact that the original 
 single evagination has now become subdivided into two smaller 
 sacs separated by a marked thickening in the original diver- 
 ticulum. This is shown in figure 41. 
 
 EP 
 
 Fig. 39 The pineal body in Cavia cobaya, according to d'Erchia, 1896. 
 Ds , dorsal sac; Ch., commissura habenularis; Sch., pars intercalaris; Ep., 
 epiphysis cerebri; M, midbrain. 
 
 In so far as is known no similar occurrence has been noted in 
 mammals with the exception of a single report by Cut ore 74 in 
 the new-born Bos taurus in which two distinct evaginations in 
 the epiphyseal complex were observed. This appearance was 
 interpreted by Cutore as indicative of an anlage both for the 
 pineal and parapineal organs, and if such an interpretation 
 seems acceptable, it might be applied to the appearances just 
 mentioned in the embryos of the domestic cat. The tendency 
 for this double diverticulum to persist through the development 
 
74 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 of the later stages in the cat is shown in figure 42, illustrating the 
 conditions in a 70 mm. embryo. Models by one of the authors 
 show the existence of this twofold structure in the cat as late as 
 120 mm. embryo. 
 
 39 
 
 25 
 
 35 
 
 Fig. 40 Mesial view of forebrain reconstruction of 30 mm. cat embryo. X 50. 
 The unshaded area shows the cut surfaces of the reconstruction, according to 
 Tilney, 1915 
 
 2, chiasmatic process; 4, chiasm; 5, corpus interpedunculare; 7, epiphysis; 9, 
 foramen of Monro; 11, infundibular stem; 12, infundibular canal; 13, infundibular 
 process; 20, lamina terminalis; 25, mammillary region; 32, post-chiasmatic emi- 
 nence; 33, post-chiasmatic recess; 34, post-infundibular eminence; 35, post-in- 
 fundibular recess; 39, dorsal sac; 40, recess of the infundibular process; 41 supra- 
 optic crest; 42, supra-optic recess. 
 
 The most recent study of the pineal region in mammals is that 
 of John Warren, 417 in which he brings to a conclusion his excel- 
 lent series of papers upon the interpretation of this region of 
 the brain in vertebrates. Of the human embryo he gives the 
 following description (fig. 43) : 
 
THE PINEAL BODY 
 
 75 
 
 The primary arches can be demonstrated in early human embryos 
 from 10 to 15 mm. in length. 
 
 Of the embryos of 15 mm. and over examined there were about thirty 
 in which the brain was in suitable condition to warrant making obser- 
 vations, and in addition to these a number of others were studied but 
 excluded on account of injury or distortion of the forebrain. In the 
 thirty specimens only eight showed any possible signs of a paraphysis 
 and most of these were mostly rudimentary in character. By counting, 
 every possible case we get a result of 27 per cent. The fact remains, 
 
 -20 
 
 Fig. 41 Mesial view of forebrain reconstruction of 51mm. cat embryo X 50. 
 The unshaded area shows the cut surfaces of the reconstruction, according to 
 Tilney, 1915. 
 
 2, chiasmatic process; 4, chiasm; 5, corpus interpedunculare; 7, epiphysis; 9, 
 foramen of Monro; 11, infundibular stem; 13, infundibular process; 20, lamina 
 terminalis; 27, mammillary body; 32, post-chiasmatic eminence; 33, post-chias- 
 matic recess; 35, post-infundibular recess; 36, post-infundibular evagination; 39, 
 dorsal sac; 40, recess of the infundibular process; 42, supra-optic recess 
 
76 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 however, that the structure can be found in human embryos, though 
 in a rudimentary and inconstant condition. 
 
 The so-called postvelar tubules or diverticula can be clearly fol- 
 lowed in every degree of complexity in embryos of 19 mm. up to 44 
 mm. and appear in every specimen studied in those stages. They 
 
 24 
 
 42 
 
 38 
 
 42 Mesial view of forebrain reconstruction of 70 mm. cat embryo. X 25. 
 The unshaded area shows the cut surface of the reconstruction. According to 
 Tilney, 1915. 
 
 2, chiasmatic process; 4, chiasm; 5, corpus interpedunculare; 7, epiphysis; 9, 
 foramen of Monro; 13, infundibular process; 24, midbrain; 27, mammillary body; 
 32, post-chiasmatic eminence; 33, post-chiasmatic recess; 34, post-infundibular 
 eminence; 35, post-infundibular recess; 38, pre-chiasmatic recess; 40, recess of 
 infundibular process; 41, supra-optic crest; 42, supra-optic recess. 
 
 begin at the diencephalic lip of the velum, have definite limits and 
 involve a relatively short extent of the oral end of the diencephalic 
 roof-plate. They always appear as outgrowths from the brain roof 
 and are to be distinguished from ingrowths due to plexus formation. 
 
 Warren's 417 description of the conditions in the sheep is as 
 follows : 
 
THE PINEAL BODY 
 
 77 
 
 The primary arches consist of the paraphyseal arch, the post velar 
 arch, the epiphyseal arch and the pars intercalaris (synencephalic arch) 
 and together with the velum are formed in the roof of the forebrain of 
 early sheep embryos. 
 
 The paraphysis can be followed in practically all sheep embryos 
 from 20 mm. up to 48 mm. It is characterized by its short, broad, and 
 irregular outline and its solid structure, the cavity being in most cases 
 reduced to a minimum. 
 
 P.V.A. 
 
 Fig. 43 Reconstruction showing development of the pineal region in man. 23 
 mm. embryo, according to John Warren, 1917. 
 
 L.T., lamina terminalis; P., paraphysis; V., velum; P.V.A. , Post-velar arch; 
 E., epiphysis; P.C., posterior commissure. 
 
78 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 The diencephalic choroid plexus and lateral telencephalic plexuses 
 are well marked and develop essentially as described in other verte- 
 brates. There is no trace of the median telencephalic plexus so notice- 
 able in Amphibia. 
 
 The epiphysis forms a short hollow stalk with thick walls and in- 
 clined slightly backward over the posterior commissure. 
 
 . The superior and posterior commissures are formed as in other 
 vertebrates. The posterior commissure is characterized by its pre- 
 cocious development and by the extent that it invades the pars inter- 
 calaris of the forebrain in early embryos (fig. 44). 
 
 It will be observed that in the ontogenesis of each element in 
 the epiphyseal complex, three distinct parts may be discerned in 
 each of the two organs entering into it. Thus, the pineal organ 
 may have an end-sac, a stalk, and a proximal portion, and the 
 same is true of the parapineal organ. Considered in the light 
 of comparative embryology, it will be seen that the most con- 
 stant part throughout the phylum is the proximal portion of 
 the pineal organ. This, beginning with a moderate prominence, 
 as in the cyclostomes, rises to a very prominent element in sela- 
 chians and maintains this prominence with somewhat of an 
 increase in its importance throughout the entire series, with the 
 single exception of crocodilia, in which the pineal body is said 
 by Sorensen 363 to be entirely wanting. On the other hand, the 
 proximal portion of the parapineal organ shows a strikingly low 
 percentage of occurrence throughout the phylum. It may 
 perhaps be accredited to the cyclostomes, if one takes into 
 account the thickened portion of the unusually large commissura 
 habenularis, but thereafter in the series it seems to disappear 
 entirely. 
 
 The next most constant structure in the epiphyseal complex 
 is the end- vesicle of the pineal organ. This maintains a high 
 degree of prominence in cyclostomes, selachians, ganoids, teleosts, 
 urodeles and anura. It shows a conspicuous tendency to atten- 
 uate in the prosaurians and saurians and finally in the ophidians, 
 and in all the orders thereafter it is notable for its absence. The 
 analogue of the pineal end-vesicle, namely, the parapineal end- 
 vesicle, is much more irregular in its occurrence throughout the 
 phylum, but on the other hand, in certain forms it presents such 
 
THE PINEAL BODY 
 
 79 
 
 striking characteristics as to make it one of the most prominent 
 and important elements in the epiphyseal complex. Its appear- 
 ance in cyclostomes is almost as striking as the pineal end- vesicle, 
 but its tendency to irregularity is noted by a complete absence 
 
 P.O. 
 
 KM. 
 
 O.C. 
 
 
 Fig. 14 Reconstruction showing the development of the pineal region of a 
 sheep embryo of 48.4 mm., according to John Warren, 1917. 
 
 ' F.M., foramen of Monro; P., paraphysis; V., velum; S.C., commissura hi 
 ularis; E., epiphysis; P.O., posterior commissure. 
 
89 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 in the selachians. It makes a somewhat abortive appearance in 
 the ganoids and teleosts. In urodeles and anura it disappears 
 altogether but when again it does occur as a feature of the 
 epiphyseal complex, it has assumed such proportions as to 
 make it by far the most prominent structure in this area of the 
 brain. In the prosaurians and the saurians, it is a most con- 
 spicuous element. As may easily be presumed, the pineal stalk 
 and its analogue, the parapineal stalk, follow very closely the 
 frequency of occurrence of the two end- vesicles. Thus the 
 pineal stalk is present in cyclostomes, selachians, ganoids, 
 teleosts, urodeles, anura, prosaurians and saurians, but disap- 
 pears in the higher forms. The parapineal stalk is present in 
 the cyclostomes, but does not appear in selachians. It has an 
 abortive form in ganoids and teleosts, is absent in urodeles and 
 anura, occurs in its most marked representation in prosaurians 
 and saurians, and thereafter disappears altogether. 
 
 6. THE COMPARATIVE ANATOMY AND HISTOLOGY OF THE 
 EPIPHYSEAL COMPLEX 
 
 In the light of the embryological development of the epiphy- 
 seal complex, the difficulties in the adult morphology of these 
 organs are much diminished. The following description will 
 deal with the comparative anatomy and histology of the two 
 epiphyseal elements in the different classes of vertebrates and 
 will be based upon the observations of the different species 
 already investigated. 
 
 1. The comparative anatomy and histology of the epiphyseal 
 complex in cyclostomes 
 
 The pineal organ in cyclostomes presents the three charac- 
 teristic parts, namely, a proximal portion, a stalk, and an end- 
 vesicle. Each of these is more or less highly specialized. The 
 end-vesicle has the form of a small elliptical vesicle. In its longest 
 diameter cephalocaudad, it is 0.35 mm. in length. This measure- 
 ment was made in Petromyzon by Studnicka. 384 It presents 
 
THE PINEAL BODY 
 
 81 
 
 certain parts, as for example, a dorsal wall and a ventral wall, 
 which are to be distinguished from each other by certain histo- 
 logical features. These two walls bound a cavity or lumen 
 concerning which there has been much discussion and to which 
 the name of atrium is usually applied. Ahlborn 2 in 1883 states 
 that this atrium presents a peculiar lacunar appearance. 
 
 Fig. 45 Cross section of the epiphyseal complex in Petromyzon, according to 
 Ahlborn, 1883. 
 
 Po., pineal organ; Ds., dorsal sac; Pp., parapineal organ; Ha., habenular 
 ganglion. 
 
 Beard 18 in 1889 thought the atrium contained a coagulated 
 fluid, and Owsiannikow 295 in 1888 was of the same opinion. 
 Gaskell, 145 however, in 1890 found that the atrium of the pineal 
 organ in Ammoccetes was in reality filled with cellular tissue 
 and, according to this observer, the pineal organ in these forms 
 had a general structure which was similar to the composite 
 eye of Arthropods. Leydig 239 in 1896 found the atrium filled 
 with what he calls secretory fibers extending inward from the 
 retinal cells of the organ. Studnicka 384 in the later stages of 
 Ammoccetes found in the lumen of the end-vesicle a peculiar, 
 
 MEMOIR NO. 9 
 
82 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 fibroid, hyaline substance attached to the free end of the cells in 
 the retina. This took on the form of a coagulum in the semifluid 
 contents of the atrium. Later Studnicka 388 in 1899 described in 
 Petromyzon marinus similar hyaline bodies and showed that they 
 were the thickened extremities of the retinal cells projecting into 
 the lumen of the end- vesicle. 
 
 ^ f <^~r^'T^TT :r ?~r^^ 
 
 \ 
 
 Pell- -i'\W 
 
 pp 
 
 Fig. 46 Sagittal section of the epiphyseal complex of Petromyzon flaviatilis 
 showing syncytial masses in the Atrium, according to Studnicka, 1899. 
 Pell., pellucida; Po., pineal organ; Ret., retina; Pp., parapineal organ. 
 
 In this way these processes from the retinal cells formed a 
 virtual syncytium which almost completely fills the atrium. Of 
 the two walls forming the end-vesicle, the ventral wall presents 
 certain characteristics which seem to justify the recognition in 
 it of a retinal structure. For this reason the ventral wall is 
 known as the retina of the pineal organ in cyclostomes. The 
 dorsal wall has an entirely different structural character, and 
 because it is quite without pigmentation is known as the pellucida. 
 
THE PINEAL BODY 83 
 
 The retina of the pineal organ in cyclostomes shows its most 
 marked development in embryonic and larval stages. Beard 17 
 in 1887 found in Ammocoetes rod cells, and Owsiannikow 295 in 
 1888 showed in Petromyzon fluviatilis that there were five dis- 
 tinct layers of cells and fibers in the retina. The first of these 
 layers consisted of nerve fibers; the second, of large nerve cells; 
 the third was fibrous; the fourth consisted of small cells inter- 
 spersed among the large rod-shaped cells, and the fifth was an 
 ependymal layer. Gaskell 145 in 1890 was able to find rod cells 
 only in the retina of Ammoccetes, and he was of the opinion 
 that the so-called pineal eye in this form was a compound struc- 
 ture in which the light-receiving bodies were formations com- 
 parable to the rhabdites of the Arthropod eye. Studnicka 
 ('93)384 recognized four layers of cells and fibers in the retina of 
 cyclostomes. The first of these was a layer of nerve fibers, the 
 second were basal cells, the third small cells, and the fourth, 
 large cylindrical cells. Leydig 239 in 1896 found two types of 
 cells, an inner cylindrical and an outer layer of round cells. 
 Retzius, 331B however, in 1895, could find no evidence of the sensory 
 organ in the so-called pineal eye of cyclostomes and he did not 
 consider it to be an eye. Mayer 264 in 1897 found ganglionic 
 cells in the retina, and Studnicka 388 in 1899 found still more 
 evidence of the retinal nature of the ventral wall of the end- 
 vesicle. 
 
 The pellucida becomes best developed in Petromyzon marinus, 
 for the dorsal wall of the pineal organ appears in the more or less 
 constant form of a plane or convexed lens, the flattened surface 
 of which is ectally directed. In Petromyzon planeri and fluvia- 
 tilis, the pellucida is extremely irregular in its thickness as well 
 as in its form. It must not, therefore, be maintained that even 
 in those forms where the pellucida has a lenticular shape and 
 arrangement that it is actually a lens structure. One feature 
 about it, however, suggests that it is an organ designed for the 
 transmission of light rays, namely, its almost complete lack of 
 pigment except perhaps at the peripheral edges where it passes 
 over into the ventral wall or so-called retina of the pineal eye. 
 This lack of pigment led Carriere 57 in 1890 to call the dorsal wall 
 
84 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 of the pineal organ the pellucida. Histologically the pellucida 
 is, according to Ahlborn 2 made up of cells of considerable size 
 together with connective tissue. Owsiannikow 296 found both 
 fibers and small cells. Whitwell 421 and Beard 18 in 1888 found 
 
 . i 
 
 
 Fig. 47 Retina and pellucida of the pineal organ in a full-grown Petromyzon 
 marinus, according to Studnicka, 1899. 
 Pell., pellucida; Ret., retina. 
 
 that the pellucida consisted of cylindrical cells. Gaskell 145 in 
 1890 observed cylindrical and small cells, and Studnicka 388 as 
 well as Retzius 331B found that the structure was made up almost 
 exclusively of large cylindrical cells. 
 
THE PINEAL BODY 85 
 
 The white pigment of the retina. Mayer 265 in 1864 observed 
 that the epiphyseal complex in Petromyzon contained many 
 calcium bodies. Subsequently Ahlborn 2 made the observation 
 that there were a large number of small bodies of a peculiar 
 white substance which he called the white pigment and regarded 
 it as similar to the brain sand of the higher vertebrates. This 
 white substance filled in the cells of the retina in such a way as 
 to prevent the passage of transmitted light and to give the 
 appearance of a glistening white when illuminated. Accord- 
 ing to Studnicka, 388 this pigment does not appear in Ammoccetes 
 younger than those of 50 mm. in length, but thereafter gradually 
 increases in amount until the adult form is attained. Ley dig 239 
 in 1896 differentiated two kinds of pigment bodies those which 
 are small in amount, of a dark brown black color and those of 
 the second type which by transmitted light appear to be a 
 brownish yellow. By direct light these pigments appear to be 
 white. 
 
 The stalk of the pineal organ in cyclostomes. In cyclostomes 
 the pineal stalk becomes much reduced in size and it completely 
 loses its lumen in the adult. It becomes conspicuous, however, 
 by the development in it of certain nerve fibers whose collected 
 bundle was first called by Leydig 239 in 1896 the 'Zirbelnerv.' 
 This structure, later in 1898, was called by Gaupp 147 the tractus 
 pinealis and finally the nervus pinealis by Studnicka. 388 This 
 pineal nerve established a fiber connection between the peculiar 
 organ situated beneath the roof-plate and known as the pineal 
 eye in cyclostomes, and the roof of the brain. The fibrous 
 nature of its structure was first observed by Whitwell 421 in 1888. 
 Owsiannikow 295 noted that in addition to the nerve fibers there 
 were to be observed in the pineal stalk a bundle of fine nerve 
 fibers. The diameter of these fibers, according to his measure- 
 ment, was 50 micra. Running with the nerves were numerous 
 blood vessels. Gaskell 145 could not distinguish whether nerve 
 fibers or processes of cells made their course within the nerve 
 sheaths. It was only at the entrance of the nerve into the eye 
 that he found a lumen. Studnicka, 388 however, maintained that 
 the stalk was an actual nerve and therefore applied to it the term 
 
86 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 nervus pinealis. He was able to trace the nerve fibers from the 
 so-called retina of the pineal eye into the stalk. Retzius 331B in 
 1895, using Golgi preparations in Ammoccetes, was able to 
 demonstrate the actual presence of nerve fibers of the pineal 
 nerve which he followed from the pineal organ to the brain. 
 This observation in similar preparations was confirmed by 
 Mayer 264 in 1897. Leydig 239 in 1896 found in Petromyzon 
 fluviatilis that nerve fibers were present only in the proximal 
 third of the stalk, while Johnston 195 in 1902 in Lampelra wilderi 
 found that the nerve fibers in the proximal portion of the stalk 
 seemed to be obliterated in some preparations. The pineal 
 nerve has a definite sheath of its own consisting of elements simi- 
 lar to those covering the brain. There is a membrana limitans 
 externa composed of neuroglia. Surrounding this is a layer of 
 pia mater and still more externally a process from the dura 
 mater. 
 
 The central endings of the nervus pinealis have been traced 
 by Ahlborn 2 and Gaskell 145 to the posterior commissure. Gaskell 
 showed that the nerve was connected with the right habenular 
 ganglion and that this nerve structure was, therefore, the optic 
 ganglion of the pineal eye. Studnicka 388 followed some of the 
 fibers to the inner portion of the posterior commissure. He 
 thought that the pineal nerve ended in the left habenular ganglion 
 while the nerve of the parapineal organ ended in the right struc- 
 ture of this name. Mayer 264 traced the fibers by means of silver 
 impregnation to the posterior commissure. The proximal 
 portion of the pineal organ in cyclostomes is much reduced in 
 size because of the close approximation between the posterior 
 commissure and the commissura habenularis. A small recess, 
 however, marks the position of the proximal portion in these 
 forms and is situated between the two commissures just men- 
 tioned. This is the recessus pinealis. The pineal organ in 
 cyclostomes has been called the epiphysis, the epiphysis cerebri, 
 and the superior vesicle of the epiphysis, according to Ahlborn 
 in 1883.* 
 
 The parapineal organ in cyclostomes. The more cephalic of 
 the two epiphyseal elements in cyclostomes has been called by 
 
THE PINEAL BODY 
 
 87 
 
 Studnicka 388 the parapineal organ. According to Ahlborn, 2 it 
 was the inferior vesicle of the epiphysis. Owsiannikow 295 termed 
 it the visceral vesicle, while it was called by Kupffer 222 the para- 
 physis. It presents an end-vesicle, a stalk, and a proximal 
 portion. It its general form it resembles the pineal organ and is 
 situated as a more or less distinct vesicle between the pineal 
 organ and the roof of the brain in the region immediately cephalad 
 to the habenular ganglion and the commissura habenularis. 
 The vesicular portion is in relation with the habenular ganglion, 
 being situated dorsal to it, while the stalk and proximal portion 
 are in relation with the commissura habenularis. In size the 
 parapineal organ is considerably smaller than the pineal organ, 
 and though it varies considerably in this respect, the following 
 tabulation made by Studnicka 388 shows the general dimensions 
 of the organ in Ammocoetes and Petromyzon planeri. These, 
 figures apply to the end-vesicles. 
 
 
 PINEAL ORGAN 
 
 PARAPINKAL ORGAN' 
 
 23 mm Ammocoetes 
 
 mm. 
 23 
 
 mm. 
 
 105 
 
 26 mm Ammocoetes 
 
 15 
 
 12 
 
 30 mm Ammocoetes 
 
 15 
 
 09 
 
 49 mm Ammocoetes 
 
 0.22 
 
 15 
 
 94 mm Ammocoetes 
 
 24 
 
 14 
 
 117 mm. Ammocoetes 
 
 0.31 
 
 0.20 
 
 Petromyzon planeri 
 
 0.35 
 
 0.25 
 
 
 
 
 Ahlborn 2 in 1883 found that the parapineal organ in general 
 has the same form, although it is smaller than the pineal organ 
 while the cellular elements in the two structures correspond very 
 closely. The lumen of the parapineal organ contains a fibrous 
 tissue having many histological features in common with that in 
 the pineal organ. Beard 18 in 1889 found the parapineal organ 
 in Ammocceies only a little less developed than the pineal 
 organ, in which opinion Gaskell 145 concurs. In Petromyzon 
 fluviatilis, Owsiannikow 295 in 1888 found that the parapineal 
 organ was smaller than the pineal organ, but in no other way 
 different from the latter. The end-vesicle contained a retina 
 
88 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 in which there were several layers of cells, including rod- and 
 cylindrical-shaped cells measuring from 7.4 to 8.3 micra in 
 diameter. There were also some larger cells scattered among 
 the rod cells with a mean diameter of 14 micra. He found in 
 the retina many nerve fibers which made their way into a definite 
 fasciculus constituting a parapineal nerve. Studnicka 388 did 
 not agree wholly with Owsiannikow in the idea that the para- 
 pineal end-vesicle was as well developed as the corresponding 
 structure of the pineal organ. He states that the difference 
 between these two structures is the fact that the parapineal 
 
 Pell 
 
 Ret 
 
 Fig. 48 Sagittal section of the pineal and parapineal organs in Ammocoetes 
 with silver impregnation, according to Retzius, 1895. 
 
 Ls., lamina terminalis; P/., paraphysis; Pp., parapineal organ; Ha., habenular 
 ganglion; Ret., retina; Pell., pellucida; N .pin., pineal nerve. 
 
 end-vesicle is not as highly developed a retinal structure as is 
 the case with the pineal end-vesicle. Studnicka, however, finds 
 that there is in the dorsal wall of the parapineal vesicle a definite 
 pellucida made up of several layers of cells. Those cells iden- 
 tified in the retinal layer by Owsiannikow 295 and Studnicka 388 
 -as the rod cells were recognized by Retzius 331B in 1895 by means 
 of the Golgi method as bipolar cells. 
 
 By this method Retzius 3313 was able to trace nerve fibers which 
 took origin in the left habenular ganglion and passed to the 
 parapineal end -vesicle. Leydig 239 in Petromyzon fiuviatilis 
 found that the parapineal end-vesicle was less developed, but at 
 
THE PINEAL BODY 89 
 
 its base he was able to discern fibers which seemed to cross to 
 the opposite side. These nerve fibers extended backward from 
 the cells in the parapineal organ. Ley dig was unable to identify 
 any structure which he considered a retina or a lens. The stalk 
 in the adult form becomes reduced to a mere strand containing 
 fibers which by many authors are considered to be nerve fibers. 
 The primitive lumen present in the stalk of the parapineal 
 organ very early disappears and the proximal portion rapidly 
 becomes inconspicuous and finally is lost by the marked develop- 
 ment of the commissura habenularis. 
 
 The majority o;f investigators who have studied this part of 
 the brain in cyclostomes are in accord along several general 
 lines. They believe that the cells found in the parapineal 
 end-vesicle are ependymal cells, spindle or rod cells, and some 
 sensory cells. It is also their opinion that there are nerve fibers 
 connecting these cells situated among which are larger ganglionic 
 elements from which the fibers may take their origin. In a 
 general way the same constituents occur in the retina of the 
 parapineal organ as are present in the pineal organ. The main 
 differences between these two structures consist in the size and 
 disposition of their respective elements. In the adult the para- 
 pineal organ is situated upon the most anterior portion of the 
 membranous forebrain roof while directly in front of it is the 
 paraphysis and above it the pineal vesicle. Situated in this 
 position the two end-vesicles of the epiphyseal complex have 
 the appearance of a pair of eyes which are rudimentary and 
 which, in attempting to assume visual function, have morpho- 
 logically fallen short in the attainment of that object. It should 
 be noted that their position places them in the midsagittal 
 plane, one behind the other, and that according to the most 
 reliable evidence concerning cyclostomes available at the present 
 time, there is no definite tendency toward lateralization in one 
 or the other of these elements in the epiphyseal complex. The 
 two end-vesicles, practically in contact with each other, occupy 
 a deep fossa formed by a depression on the inner surface of the 
 skull. This fossa is especially well marked in adults and more 
 particularly in Petromyzon marinus. 
 
90 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 What has been termed a parietal cornea of the pineal eye con- 
 sists of a layer of almost fiberless tissue of considerable thickness 
 between the dorsal surface of the pial capsule and the inner 
 surface of the bony depression in the skull. The epidermis 
 immediately above this so-called cornea is quite without pig- 
 ment, forming a small, circular area in the frontal region of the 
 head situated almost immediately in the midsagittal line. This 
 area was recognized long before its significance was understood 
 and was described by Whitwell 421 in 1888, by Ahlborn 2 in 1883, 
 and by Gage 135 in 1893. Gaskell 145 in 1890 erroneously likened a 
 cranial thickening above the pineal organ in Ammoccetes to the 
 cuticular lens of Arthropods. Studnicka 384 in 1893 found that 
 the cornea is discernible in the 25 mm. Ammoccetes. Gaskell, 145 
 in his discussion of the origin of vertebrates from a crustacean- 
 like ancestor, makes the statement that in Ammoaztes there 
 are two pineal eyes, one, dorsally placed, much larger and in- 
 tensely white in color, lies in front of the right habenular ganglion. 
 The other, ventrally placed, is an insignificant structure. The 
 first is similar to the crustacean parietal eye in its pigmentary 
 character. The second is similar to this eye in Crustacea because 
 of the termination of the nerve endings with the attached rhab- 
 dites. According to Gaskell, the type of eye is clearly arthro- 
 podic. The arrangement of the nerve endings, the shape of the 
 internal cavity, and the position and simplicity of the attached 
 rhabdites all point to larval characteristics and, therefore, to an 
 ancient type. The anterior wall is not a lens. Gaskell believes 
 the lens is cuticular in character and, if so, this is all the more 
 reason for believing that the pineal eye is definitely arthropod in 
 type. 
 
 Much emphasis has been laid upon the occurrence in cyclo- 
 stomes of these two structures which have so many characteristics 
 suggestive of visual function. The statement has been made 
 that this is competent evidence upon which to establish the 
 claim that in vertebrates the parietal or third eye was primi- 
 tively paired. It is to be noted, however, that in no other class 
 of vertebrates does the duality of the parietal visual apparatus, 
 if such indeed it may be considered, attain such a high degree of 
 
THE PINEAL BODY 91 
 
 development. One or the other element of the epiphyseal com- 
 plex may show the tendency toward the development of visual 
 characteristics, but in no other form do both of these elements 
 take on these features so suggestive of visual function. 
 
 Differences observed in the epiphyseal complex of the various 
 species of cyclostomes already investigated. Although all of the three 
 European forms of Petromyzon have been carefully studied by 
 several investigators, the differences between them are not 
 striking. This statement also applies to the North American 
 form, Lampetra wilderi, described by Johnston 195 in 1902. 
 
 1. Petromyzon planeri. Ahlborn ('83) , 2 Beard ('89), 18 Whit- 
 well, ('88) 421 and Studnicka ('93) , 384 The epiphyseal complex as 
 a whole is not separated as far from the brain as in other forms, 
 due to the fact that the paraphysis and dorsal sac are but little 
 developed. The parietal fossa is very shallow and is absent in 
 Ammoccetes as is also the white pigment. 
 
 2. Petromyzon fluviatilis. Ostroumoff ('87), 291 Owsiannikow, 
 ('88) , 295 Leydig, ('96) 239 and Studnicka ('99). 388 In this form the 
 evagination of the roof is very high and the fossa in the skull of 
 considerable depth. The atrium contains a definite syncytium 
 made up of processes not only from the retinal cells, but also 
 from those situated in the pellucida as well. 
 
 3. Petromyzon marinus. Studnicka ('99). 388 Although the 
 dorsal sac is extremely high, the depression in the skull is no 
 deeper than in the case of Petromyzon fluviatilis. 
 
 4. Petromyzon wilderi. Johnston ('02). 195 In this form the 
 stalk of the pineal organ has not the significance as in other 
 forms, for the pineal nerve is absent and the stalk contains no 
 nerve fibers. 
 
 5. Mordacia mordax. Spencer ('90). 369 In this 'form the 
 pineal organ presents a thin, pigmented upper wall correspond- 
 ing to the pellucida of Petromyzon and a thicker ventral* wall in 
 the form of a retina. No definite statement is made as to the 
 presence of an atrium, although the lumen of the organ is said 
 to be filled by a coagulum. There is no evidence of any para- 
 pineal organ, but on the surface of the head, midway between 
 the paired eyes, there is a parietal spot. 
 
92 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 6. Myxine gluiinosa (Bdellostoma). Kupffer ('04). 226 In this 
 form there is no anlage of the epiphysel complex whatsoever. 
 The roof is entirely flat, but in spite of the absence of the epi- 
 physeal complex, both habenular ganglia are present. Such 
 descriptions of the epiphysis in Myxine as appear in the litera- 
 ture seem to be an error. Andrae Retzius 33lA in 1822 described 
 the pineal body in connection with the habenular ganglion, 
 interpreting the latter to be the epiphysis. Ley dig 239 in 1896 
 believed that he had found in Myxine the pineal body, but in 
 reality mistook a large lymph space near the surface of the 
 head for this organ. Studnicka, 388 however, in his studies was 
 unable to find any evidence of the pineal body in Myxine. 
 
 2. The comparative histology and anatomy of the epiphyseal 
 complex in selachians 
 
 Since the pineal organ is the only part of the epiphyseal com- 
 plex to make its appearance in selachians, the structure is much 
 more simple than in cyclostomes. Furthermore, such parts of 
 the pineal organ as do develop in selachians are relatively rudi- 
 mentary. All of the three usual elements of the pineal organ, 
 however, may be identified; that is to say, a hollow end-vesicle, 
 a stalk, and a proximal portion. The end-vesicle in no instance 
 presents the two distinct walls, namely, the ventral and dorsal 
 walls distinguishable in cyclostomes, and the end-sac itself is 
 much smaller than in the forms already considered. Slight 
 differences in the thickness of the wall of the end-vesicle may be 
 observed in different places, but with no great uniformity. In 
 consequence of this lack of differentiation, there is no evidence 
 of the formation of a retina, of a pellucida, or of a white sub- 
 stance, nor do any nerve fibers make their appearance in con- 
 nection with the end- vesicle. In fact, it is a question whether 
 the pineal organ of selachians is a primitive structure or one 
 that is distinctly retrograde. In form there may be a consider- 
 able difference in the terminal vesicle; it may be wedge-shaped, 
 cylindrical, conical, or flattened, but in all instances it is hollow, 
 containing a lumen, in spite of the statement of Cattie 60 to the 
 contrary in his descriptions of Mustelus, Raia, and Acanthias. 
 
THE PINEAL BODY 93 
 
 Frequently the wall of the vesicle presents reduplication, as in 
 the case of Spinax niger where there is a distinct tendency to 
 tabulation, or as in Acanthias where the folding of the wall 
 results in the production of two adjacent vesicles. In a single 
 instance only is there a marked differentiation between the 
 ventral and dorsal walls. This occurs in Lamna cornubica, 
 particularly in the embryonic state, described by Carrington 58 
 in 1890. In this form the under wall was thicker than the 
 dorsal wall. Studnicka 389 found some tendency to such a dif- 
 ferentiation in Spinax. 
 
 Hist ologic ally, the walls of the end- vesicle are made of epen- 
 dymal cells, but there are no cylindrical or spindle cells to be 
 observed in this structure. The cells described in cyclostomes 
 as having prolongations of such a character as to warrant the 
 description of ciliated cells are absent in selachians so that no 
 such processes make their way into the lumen of the end-vesicle, 
 as is the case in Petromyzon. The nuclei of these cells are 
 situated at varying distances from the surface of the wall so that 
 the ependyma gives the impression of stratified epithelium, 
 whereas in reality it is a single layered epithelial structure. 
 Some cells have a rather long process which approach, but do 
 not enter, the lumen of the end-vesicle. This manifestation is 
 taken as a probable sign of an excretory function of the cells in 
 question. Galeotti 140 in 1896 described in Scyllium peculiar 
 appearances which seemed to indicate a secretory or excretory 
 activity on the part the cells in this portion of the pineal 
 organ. Among the more usual cells, according to Studnicka, 389 
 there are many smaller cells scattered here and there of a similar 
 type to the sense cells in the retina of Petromyzon. The signifi- 
 cance of these cells is not at all clear, and Studnicka himself is 
 not willing to accredit them with a definitely receptor function. 
 
 The stalk of the pineal organ. Microscopically, this appears to 
 be a long, narrow strand connecting the end-vesicle with the 
 roof-plate of the interbrain. Upon microscopic examination 
 it is found, however, to contain a central but narrow lumen, the 
 entire structure, therefore, being tubular. In most instances 
 this stalk maintains an equal diameter throughout its entire 
 
94 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 extent, although in certain cases it becomes much attenuated 
 as it approaches the end-vesicle. A few nerve fibers course in 
 the dorsal wall of this hollow stalk, but these cannot properly be 
 considered the homologue of the pineal nerve in selachians. 
 
 The proximal portion in selachians may be readily made out. 
 As the stalk approaches the roof of the interbrain, it gradually 
 becomes dilated and increased in its transverse diameter. Its 
 lumen becomes larger and the walls bounding it are thrown into 
 numerous folds. Although the transition from stalk to proximal 
 portion is gradual, it is nevertheless distinct. In a few cases 
 
 Fig. 49 End-vesicle in the pineal organ of Acanthias vulgaris, according to 
 Studnicka, 1893. 
 
 only, such, for example, as Centrophorus, described by Cattie 60 
 in 1882, is there an absence of this reduplication of the walls of 
 the proximal portion. As the dorsal wall of this portion ap- 
 proaches the posterior commissure there appear in it a few 
 strands of nerve fibers constituting what may be called the 
 tractus pinealis. It is doubtful, however, whether the com- 
 missura habenularis receives any of the fibers which enter into 
 the formation of this tract. 
 
 The sheaths of the pineal organ are the same as those in Petro- 
 myzon, namely, a membrana limitans externa, a process from 
 
THE PINEAL BODY 95 
 
 the pia mater and another from the dura mater. Some authors, 
 .among them Cattle, 60 have described a parietal foramen. In 
 Acanthias vulgar is this opening in the cartilaginous skull appears 
 to be doubled, the two openings being separated by a small, 
 cartilaginous bridge. Neither Studnicka 389 nor Ehlers 108 was able 
 to discover any such openings in the forms which they investi- 
 gated. The parietal cornea is absent and the parietal spot is 
 very infrequently observed. 
 
 Differences observed in the epiphyseal complex of the various 
 species of selachians already investigated. 
 
 ELASMO BRANCHI 
 
 1. Scyllium canicula and calulus. Balfour (78) 10 studying the 
 embryonic development; Owsiannikow ('88), 295 studying the con- 
 ditions in a 65 mm. embryo; Cattie ('82), 6 in the adult, and 
 Galeotti ('96), 14 studying the histology. The proximal portion 
 in these forms is not well developed and the end- vesicle is coni- 
 cal. The middle piece or stalk is cylindrical in shape. The 
 structure, according to Galeotti, shows stellate cells and epen- 
 dymal cells, in addition to which, there are certain cells which 
 are definitely fuchsinophile, which, according to this observer, 
 indicate secretory function because he considers these granules 
 secretory in their nature. 
 
 2. Acanthias vulgaris. Ehlers 108 in 1878 and Cattie 60 in 1882. 
 In this form the proximal portion is thicker than the stalk and 
 both are of unusual thickness for selachians. The end-vesicle, 
 according to Cattie, is solid. Its walls show much reduplication 
 and the lumen is solidly filled with a syncytium. There is a 
 definite parietal foramen. 
 
 3. Echinorhynus spinosus. Jackson and Clarke (75) 193 . The 
 pineal organ in this form is a long, strand-like body extending far 
 over the telencephalon in the midsagittal plane. 
 
 4. Galeus canis. Cattie ('82). 60 A conical end- vesicle and a 
 conical proximal portion with a strand-like stalk characterize the 
 pineal organ in this form. The end- vesicle and the stalk are 
 solid while the proximal portion retains its lumen and has, in 
 addition, many small accessory canuliculae. 
 
96 FEEDERICK TILNEY AND LUTHER F. WARREN 
 
 5. Mustelus Icevis. Cattle ('82). 60 In this form the pineal 
 organ is extremely simple, consisting of an end-vesicle, a stalk, 
 and a proximal portion. The end- vesicle is flat and shows no 
 tendency toward reduplication. 
 
 6. Centrophorus granulosus. Cattie ('82). 60 The end- vesicle 
 in this form has a hammer-shaped appearance. The stalk is 
 strand-like and the proximal portion conical. The pineal organ 
 is hollow throughout its entire course. A marked parietal 
 depression lodges the structure and this is surrounded by con- 
 nective tissue. 
 
 7. Lamna cornubica. Carrington ('90). 58 This form pre- 
 sents an end-vesicle which is conical and a stalk which is cylin- 
 drical. Both contain an irregular lumen. The ventral wall of 
 the end- vesicle is thicker than the dorsal wall. The cells in this 
 vesicle are for the most part ependymal, although there are 
 many others scattered among the cells of this character. The 
 pineal organ is lodged in a depression surrounded by connective 
 tissue and there is a corresponding slight depression in the epi- 
 thelium above the organ. 
 
 8. Spinax niger. Studnicka ('93). 384 In embryos, larval and 
 adult forms, this species presents all three portions of the pineal 
 organ. It is slender and directed at right angles to the roof- 
 plate in the embryo, is slightly bent in larval forms, and is 
 flexed at right angles in adults. The end- vesicle is pressed into 
 a cartilaginous skull, although there is no actual parietal fora- 
 men. The parietal portion consists of ependymal cells and 
 neuroglia cells. A parietal spot is present in the form of an 
 oval white area. There is, however, no parietal cornea. 
 
 9. Notidanus griseus. Studnicka ('93). 384 The entire pineal 
 organ in this form is sharply flexed forward above the forebrain. 
 The proximal part is not particularly developed, but in other 
 respects has the same general form as other species. 
 
 10. Pristiurus melanostomus. d'Erchia ('96) 109 and Minot 
 ('01). 277 Here the pineal organ extends directly forward in the 
 horizontal plane above the forebrain in the midsagittal plane. 
 The end-vesicle is much attenuated and the stalk is merely a 
 strand-like connection between the former and the roof-plate 
 
THE PINEAL BODY 
 
 97 
 
 of the interbrain. There is a small conical, proximal portion. 
 Cattie 60 states that the parietal foramen is closed only by the 
 dura mater. 
 
 RAIIDAE 
 
 1. Raia clavata. Ehlers (78) ; 108 Cattie ('82). 6 In this spe- 
 cies a thin, long stalk extends far forward and terminates in a 
 definite end- vesicle which is enclosed in a deep prefrontal fossa. 
 
 /'/" /' Os C/f 
 
 Fig. 50 The pineal region of Torpedo ocellata, according to d'Erchia, 1896. 
 
 Hm., hemisphere; Pf , paraphysis; V., velum transver um; Ds., dorsal sac; 
 Ch., commissura habenularis ; S h , pars intercalaris posterior; Cp., posterior com- 
 missure; M., midbrain 
 
 2. Raia follonica. Studnicka ('95). 385 The pineal organ here 
 is found as a thick stalk with a lumen. There is no special 
 proximal portion. In the lumen there is a syncytium. 
 
 3. Myliobatis aquila. Studnicka ('95). 385 In this form, as 
 in Raia clavata, the stalk is tubular and reaches from the inter- 
 brain to the roof of the skull. The end-vesicle is dorsoventrally 
 flattened and rests in the region of the prefrontal fossa, which 
 latter shows but a slight deepening in the skull. 
 
 4. Torpedo marmorata. Studnicka ('95). 385 In this form the 
 pineal organ fails to appear, although there are present two 
 well-developed ganglia habenulae. 
 
 MEMOIR NO. 
 
98 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 5. Torpedo ocellala. d'Erchia ('96). 109 No evidence of de- 
 velopmental differentiation into a pineal organ was found in 
 the early stages of this form. A well-developed paraphysis, 
 however, is present. 
 
 HOLOCEPHALI 
 
 1. Callorhynchus. Parker and Haswell ('97). 302 
 
 2. Chimaera monstrosa. Studnicka ('96). 386 In both of these 
 forms there is a well-defined epiphysis and a large dorsal 
 sac. The pineal organ has a form similar to other selachians; 
 that is to say, a fairly well-marked proximal portion, a long, 
 slender stalk extending forward and expanding slightly to form 
 an end-vesicle at its extremity. 
 
 In all, seventeen species of selachians have been examined; 
 that is, ten Elasmobranchs, five Rays, and two Holocephali. 
 In two species a complete absence of the pineal organ is reported, 
 namely, Torpedo ocellata and Torpedo marmorata. All of the 
 other species present a pineal organ more or less well developed. 
 In one form, that is, Galeus cam's, histological evidence has been 
 presented showing that there is some reason to believe that a 
 secretory function obtains in the pineal organ of this form. 
 Wherever mention is made of the paraphysis it seems to be an 
 organ of considerable size. 
 
 3. Comparative anatomy and histology of the epiphyseal complex 
 
 in ganoids 
 
 In all the species of Ganoids there develops a fairly well- 
 marked pineal organ. In one form only, namely, Amia, is there 
 any indication of the presence of a parapineal organ. Stannius, 373 
 giving the first description of the structure of the parapineal 
 organ in Acipenser sturio in 1854, states that the structure is a 
 wide evagination extending from the roof of the interbrain and 
 connected with the commissura habenularis. It reaches for- 
 ward to a fossa in the roof of the skull. Cattie 60 in 1882, also in 
 Acipenser sturio, and Goronowitsch 153 in 1888, on Acipenser 
 ruthenus, gave similar descriptions of the pineal organ. Gar- 
 man 143 in 1896 and Johnston 194 in 1901 by means of the Golgi 
 
THE PINEAL BODY 
 
 99 
 
 method described the structure in Acipenser rubicundus. Both 
 observers were able to differentiate a saccular proximal portion 
 resembling the recessus pinealis, a thin, dorsoventrally extend- 
 ing stalk, the latter producing a groove in the dorsal surface 
 of the dorsal sac, and finally an end-vesicle greatly dilated. 
 The end-vesicle was of considerable size and contained a well- 
 marked cavity. 
 
 Its walls showed no tendency to differentiation into a dorsal 
 pellucidal layer or a ventral retinal layer. According to Stud- 
 nicka, 386 the entire end- vesicle consists of rather long cylindrical 
 
 Hm 
 
 Opt 
 
 Fig. 51 The pineal region in Polyodon folium, according to Garman, 1896. 
 Olf., olfactory lobe; Opt., optic nerve; Hm., hemisphere; Po., pineal organ; 
 St., stalk. 
 
 cells with a generally oval nucleus and two processes, one a 
 slender extension reaching in toward the lumen of the pineal 
 organ and the other a more diffuse ending, extending toward 
 the ectal surface of the wall. Scattered here and there among 
 these cells, which are in the majority, are a number of large 
 elements more distinctly oval in character with a rounded 
 nucleus situated near the center. Some smaller elements are 
 also found scattered more numerously among both types of 
 cells. Studnicka describes them, first, as ependymal cells; 
 second, as sense cells, a larger-sized cell which he thinks may 
 
100 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 be ganglionic cells, and, third, neuroglia cells which are smaller 
 and generally more deeply situated elements in the walls of the 
 end-vesicle. The stalk is strand-like in appearance and may 
 
 * b 
 
 Fig. 52 a, Pineal organ in Acipenser rubicundus. b, Pineal organ in Polyo- 
 don folium. 
 
 contain a lumen in part of its extent or else running the entire 
 length from the roof-plate end-vesicle. Its walls are made up 
 of small neuroglia cells, while in the more dorsal of the two walls 
 
THE PINEAL BODY 
 
 101 
 
 Johnston 194 found a number of nerve fibers constituting a layer 
 which extends from the proximal portion to the commissura 
 habenularis, where it apparently undergoes decussation form- 
 ing the so-called decussatio epiphysis. These observations were 
 made by means of the Golgi method. Other fibers end freely 
 between the cells of the stalk. These cells, Johnston thinks, are 
 rudimentary or degenerated nuclei, perhaps related to the pineal 
 
 Fig. 53 Histological structure of the wall of the pineal organ in Acipensei 
 sturio, according to Studnicka. 1893. 
 
 eye. He found a third type of fibers in a decussation which 
 comes into relation with the ganglia habenulae. Herrick 177 in 
 1891 also mentioned such fibers in Acipenser. The proximal 
 portion consists, in the main, of small neuroglia elements with 
 some nerve fibers running in it, as already described. Stud- 
 nicka 386 does not think that there is any indication of a glandular 
 activity in this part of the pineal organ which is in any way 
 comparable to that of the proximal portion in the pineal organ 
 of selachians. 
 
102 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Differences observed in the epiphyseal complex in the various 
 species of ganoids already investigated 
 
 1. Acipenser sturio, ruthenus, and rubicundus. Cattle ('82), 60 
 Goronowitsch ('88) ; 153 Garman ('96), 143 and Johnston ('01). 194 
 The conditions in these forms have been described above. 
 
 2. Lepidosteus osseus. Balfour and Parker ('82). 12 The 
 pineal organ in this form was first mentioned by these authors 
 and later by Sorensen 363 in 1894, who described the structure as 
 having a distinctly saccular form. 
 
 3. Amia calm. Goronowitsch ('88) 153 and Gage ('93). 135 
 Both of these authors showed that the pineal organ was a simple 
 sac in this species. Hill 180 in 1894 found in the embryonic stages 
 evidences of both parietal organs, namely, what he calls the 
 anterior epiphysis and the posterior epiphysis which probably 
 corresponded to the parapineal and pineal organs in Petromyzon, 
 while the anterior epiphysis is considered the homologue of the 
 parietal eye in Saurians. In the later embryonic stages the 
 connection with the brain of the anterior sac is lost. Finally 
 the pineal organ is pushed to the left side. Eycleshymer 112 
 found that the anterior organ has a lumen as late as the 15 to 
 16 mm. embryo. Nerve fibers were observed as late as the 
 12 to 13 mm. embryo going from the commissura habenularis to 
 the interior of .the anterior organ. Kingsbury 205 in 1897 observed 
 both the pineal and parapineal organs in the adult Amia. The 
 anterior organ was lying to the left of the pineal stalk and was 
 connected with the left habenular ganglion by means of a 
 thick, neural fasciculus. 
 
 4. Polyodon folium. Garman ('96). 143 This species possessed 
 processes which look like nerve fibers. These processes go 
 from the interbrain roof and extend out to an end-sac deeply 
 situated in a parietal fossa of the skull. In one case only was 
 there a complete parietal foramen. 
 
 5. Polypterus bichir. Waldschmidt ('87) 412 
 
 6. Polypterus senegalus. Waldschmidt. 412 Both of these 
 species of Crossopterygii present a pineal organ which has a 
 tubular stalk and rises above the dorsal sac, first upward, then 
 turns sharply forward to end in a slightly dilated end-vesicle. 
 
THE PINEAL BODY 103 
 
 The walls of the organ have, in addition to the usual ependymal 
 cells, some special sensory cells. In the lumen are free cells with 
 no particular syncytial formation. 
 
 In the ganoids no mention is made of any evidence indicative 
 of glandular activity. Six ganoids in all have been carefully 
 studied and in only one, as already stated, are there signs of the 
 parapineal organ, namely, in Amia, otherwise all species present 
 a pineal organ which is not as well developed as in the selachians. 
 
 4. Comparative anatomy and histology of the epiphyseal complex 
 
 in teleosts 
 
 The epiphyseal complex in teleosts differs from that in selach- 
 ians and ganoids in its greater size. In some forms, however, 
 it is only rudimentary, being but a solid bud, while in others, 
 it is a complicated end-sac. It is never in any case like an eye 
 and seldom does it come into relation with the surface of the 
 head as in the cyclostomes. The number of species already 
 examined is perhaps too limited to make certain of all of these 
 observations. The only part of the epiphyseal complex which 
 develops and appears in the adult is the pineal organ. In a few 
 instances, during the very early stages of development, there 
 is present what may be considered the anlage of the parapineal 
 organ. The parts which the pineal organ presents in teleosts 
 are an end-vesicle, a stalk, and an ill-defined proximal portion. 
 In many instances the stalk is short and the end-sac large. In 
 most species the end- vesicle is pear-shaped and connected with 
 the roof by a hollow stalk. The walls of the end- vesicle are 
 either flat or formed into many folds, thus producing lateral 
 diverticula and giving the sac the appearance of a tubular gland. 
 In some cases the end-vesicle does not develop as such, the pineal 
 organ being a broad sac connected with the brain by a slightly 
 constricted area. The entire pineal organ may be a rudiment 
 as in Syngnathus, where it is almost solid throughout its entire 
 extent. The vast majority of the cells in the end- vesicle are 
 small and set closely together. Some cells have an epithelial 
 arrangement: these are doubtless neui;oglia. The presence cf 
 
104 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 actual ganglionic cells is doubtful. Some cells observed by- 
 Hill 180 in 1894 have very long processes. Studnicka 386 observed 
 that whatever the character of the cells of the end-vesicle may 
 be, whether special sensory or not, the entire organ is not a 
 gland. By this he does not deny the possibility that the struc- 
 ture may be in part glandular. Galeotti 140 in 1896 found some 
 
 ...-Epid 
 
 Cor 
 
 St. 
 
 Pig. 54 The epiphyseal complex in Anguilla fluviatilis, according to Leydig, 
 1896. 
 
 V., velum transversum; Ds., dorsal sac; Po., pineal organ; St., stalk. 
 
 evidence of. secretory activity in the cells of the pineal organ in 
 these forms. In Leuciscus, he observed nuclei which had fuch- 
 sinophile granules and also nucleoli which later appeared in the 
 protoplasm. The product of this secretion was, in his opinion, 
 delivered to the lumen of the end-vesicle which is completely 
 surrounded by blood vessels. The stalk, when definitely pres- 
 
THE PINEAL BODY 
 
 105 
 
 ent, has a form similar in character to the end-sac and is made 
 up, in the main, of small neuroglia cells. Nerve fibers constitut- 
 ing what has been called the pineal nerve of the stalk have been 
 observed making their way to the posterior commissure. Hill 180 
 observed in Salmo purpuratus, and Studnicka 386 in Cyprinus 
 carpio, Carassius auraius, Esox lucius, and Cobitis fossilis 
 what may be termed a tractus pinealis running from the pos- 
 terior commissure through the pars intercalaris posterior to the 
 
 Epid 
 
 At 
 
 Cp 
 
 Ds Ch 
 
 Sch 
 
 Fig. 55 The epiphyseal complex in Salmo purpuratus, according to Hill, 1894. 
 
 V., velum transversum; Ds., dorsal sac; Ch., commissura habenularis; R. 
 proximal portion; Po., pineal organ; Tp., tractus pinealis; Sch., pars intercalaris 
 posterior; Cp., posterior commissure. 
 
 stalk and then in the dorsal wall of the stalk to the end- vesicle. 
 Hill says these fibers are connected with elements in the latter 
 vesicle. 
 
 With reference to the site and relation of the pineal organ to 
 the skull, it has infrequently been observed that this organ 
 occupies a prefrontal fossa. What has been designated a 
 cornea, namely, a large mass of fiberless connective tissue above 
 the end-vesicle, has been described in teleosts, but there is no 
 parietal spot in any other form thus far investigated. 
 
106 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Differences observed in the epiphyseal complex in the various 
 species of teleosts already investigated 
 
 PHYSOSTOMI 
 
 1. Esox lucius. Gottsche ('35) 154 mentioned for the first time 
 the pineal organ in this form. Stieda 378 in 1873 called it a red 
 body of very insignificant size. Cattie 60 in 1882 distinguished 
 an end-vesicle and a stalk, the former richly supplied with 
 blood and deeply sunken into a fossa in the roof of the skull. 
 He described oval ependymal cells, and pear-shaped cells in 
 the end-vesicle. The stalk was hollow and its dorsal wall con- 
 tained a tractus pinealis. There were many folds in the end- 
 vesicle. 
 
 2. Tinea vulgaris. Cattie ('82). 60 In this form there is a 
 well-defined proximal portion, which, however, is a fine strand- 
 like structure. The end-vesicle is flattened and much expanded. 
 
 3. Salmo solar. Cattie ('82). 60 This species has an end- 
 vesicle which is pear-shaped and a very short, highly vascular 
 stalk. The end-vesicle is in contact with the roof of the skull. 
 
 4. Salmo fario, purpuratus and fontinalis. Rabl-Riickhard 
 ('83) ; 319 Hill ('94). 18 These forms present a pineal organ hav- 
 ing an end-vesicle in a depression of the skull and a stalk con- 
 necting it with the posterior commissure. The stalk has a cen- 
 tral canal, the lumen of which is bounded by cylindrical cells. 
 Hill found in embryos not only the pineal organ, but the para- 
 pineal organ as well; the latter remains rudimentary. Hill 
 called the pineal organ the posterior epiphysis. It presents a 
 proximal, narrow portion and a distal, flattened end-vesicle 
 which is thick and lodged in a deep fossa of the skull. It has 
 many diverticula and is rich in blood vessels. A long canal 
 runs through the stalk; nerve fibers connecting with some of 
 these cells in the end-vesicle make their way through a portion 
 of the stalk, and a definite tractus pinealis in the dorsal wall of 
 the stalk ends in the posterior commissure. In the adult of two 
 years old, Hill described a distal end-sac which retains the em- 
 bryonic form. The rest disappears. In the distal part of the 
 sac are many cell groups containing granular or colloid masses 
 
THE PINEAL BODY 107 
 
 in irregular acini. The tractus pinealis persists. The anterior 
 epiphysis in the adult is reduced to a small mass of cells. 
 
 5. Anguilla fluviatilis. Cattie ('82) . 60 In this species there 
 is a proximal portion and a cylindrical end-sac. Ley dig 239 in 
 1896 described the end- vesicle as very much reduplicated and 
 highly vascular. Galeotti 140 in 1896 saw a clear caryoplasm and 
 no granules or nucleoli in the end-vesicle. He, therefore, con- 
 cludes that there is no evidence of secretory activity in this 
 form. 
 
 6. Clupea alosa. Cattie ('82). 60 A strand-like stalk and an 
 expanded end-vesicle are observed in this form both of which 
 are solid. 
 
 7. Clupea harengus. Holt ('91). 189 In the late larval stages, 
 the epiphysis in this species is a solid body. In younger em- 
 bryos a nerve bundle extends from the pars intercalaris up the 
 stalk. In the later stages there is a saccular epiphysis with a 
 wide lumen three or four cells deep. The lumen is filled with a 
 coagulum. The tractus pinealis is present in the dorsal wall of 
 the stalk. 
 
 8. Leuciscus rutilus. Rabl-Ruckhard ('83). 319 The distal end 
 of the organ in this form is flattened out against the inner 
 surface of the skull. There is a very thin but long stalk (fig. 56). 
 
 9. Leuciscus cephalus. Galeotti ('96) 14 found in the cells of 
 the pineal organ those above-mentioned structural peculiarities, 
 which he considered indications of secretory activity. 
 
 10. Amiurus catus. Ramsay Wright ('84). 43 The pineal 
 organ in this species is tubular and has the same thickness 
 throughout its entire extent. It ends in a fatty tissue. Its 
 end-vesicle does not reach the cranial roof. Its walls are thin 
 and form no folds. 
 
 11. Callichthys asper and litioralis. Dean ('88). 81 In both 
 of these -forms there is a parietal foramen with a retinoid tissue 
 lying beneath it. Klinckowstroem 208 in 1893 found a parietal 
 foramen closed by connective tissue in these forms. An end- 
 vesicle was located here, but showed no particular specialization. 
 
 12. Doras, Clarias, Loricaria. Dean ('88). 81 In these species 
 there is a parietal foramen. 
 
108 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 13. Coregonus albus. Hill ('91). 179 In the embryonic state 
 of this species the anlagen of the pineal and parapineal organs 
 both occur. 
 
 14. Caioslomus teres. Hill ('94) 18 found the anlagen of the 
 anterior and posterior epiphysis in embryos of this form. These 
 were almost transversely placed in relation to each other. 
 
 Front 
 
 Hm 
 
 Fig. 56 Transverse section through the end-vesicl'e of the pineal organ in Leu- 
 ciscus rutilus, according to Rabl-Riickhard, 1883. 
 Po., pineal organ; Hm., hemispheres. 
 
 15. Cobitis fossilis and barbatula. Studnicka ('96). 386 The 
 pineal organ in these species is tubular. The distal end forms a 
 large sac which lies beneath the skull. The tractus pinealis is 
 present. 
 
THE PINEAL BODY 
 
 109 
 
 16. Belone acus. Studnicka ('96). 383 In this species there is 
 a long, tubular stalk. Ependymal cells form the walls of this 
 stalk and have an arrangement reminiscent of the retinal sen- 
 sory cells of the retina of Petromyzon especially of the region of 
 the large end- vesicle (fig. 57). 
 
 17. Cyprinus carpio. Studnicka ('96). 383 The end-vesicle 
 in this form is a circumscribed dilatation and has a thin, hollow 
 
 Cr 
 
 Hn 
 
 Ch 
 
 Fig. 57 The epiphyseal complex in Belone acus, according to Studnicka, 1896. 
 
 Ls., lamina terminalis; Pf., paraphysis; D., dorsal sac; Ch., commissura ha- 
 benularis; R., proximal portion; Po., pineal organ; Cp., posterior commissure; 
 M., midbrain. 
 
 stalk, in the dorsal wall of which there courses the tractus 
 pinealis. 
 
 18. Carassius auratus. Studnicka ('96). 386 The pineal organ 
 in this form is tubular throughout its entire extent. There is a 
 tractus pinealis as usual in the stalk, but no fossa in the skull. 
 
 19. Argyropelecus hemigymnus. Handrick ('01). 168 In the 
 adult of this form both the pineal and parapineal organs appear 
 to be present. The pineal organ has a thin stalk and a large 
 
110 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 end-vesicle which is much folded and highly vascular, being 
 mushroom in shape. This sac has much to suggest glandular 
 activity. No tractus pinealis could be discovered in the stalk. 
 The end-vesicle lies beneath the roof in the frontal region and 
 there is in this particular area an actual frontal or parietal fora- 
 men. The parapineal organ is tubular in form and lies in front 
 
 Fig. 58 Cross section of pineal organ and dorsal sac in Argyropelecus hemigym- 
 nus, according to Handrick, 1901. 
 Ds., dorsal sac; Po., pineal organ. 
 
 of the pineal organ. It is shorter than the pineal organ and does 
 not reach the parietal foramen. It has a long stalk. Stud- 
 nicka 386 thinks Handrick' s parapineal organ is nothing more than 
 a peculiar formation of the dorsal sac. 
 
 20. Opsanus. Terry ('II). 392 The pineal organ in this species 
 presents an oval end-vesicle with a long slender stalk, both of 
 
THE PINEAL BODY 111 
 
 which contain a lumen, but neither have connection with the 
 third ventricle. The cavity of the pineal organ is traversed by 
 protoplasmic processes forming a dense meshwork from wall to 
 wall. Although the pineal organ is highly vascular in Opsanus, 
 it does not conform in structure to any of the known ductless 
 glands, and is, therefore, probably not glandular. There is no 
 pineal nerve, no parietal foramen or fossa, no dorsal sac or 
 paraphysis. 
 
 PV 
 
 D 
 PC Y 
 
 Fig. 59 Pineal region in an embryo of Opsanus, according to Terry, 1911. 
 
 T.R., lamina terminalis; P., paraphysis; V., velum transversum ; P.V., post- 
 velar arch (dorsal sac); S., commissura habenularis; E., epiphysis; P.O., pos- 
 terior commissure. 
 
 PHYSOCLYSTI 
 
 21. Gadus morrhua. Baudelot (70). 14 The pineal organ in 
 this species is a long, pear-shaped structure. Cattie 60 in 1882 
 distinguishes a strand-like proximal portion and an end-vesicle 
 rich in blood vessels. In the latter are round and oval nuclei 
 and round and pear-shaped cells with one or two processes. 
 
 22. Trigla hirundo. Ussow ('82). 40; A short pineal organ 
 with a hollow end-stalk is the characteristic in this species. 
 The end-vesicle is convoluted and reminiscent of the conditions 
 in the hypophysis. The cells bordering upon the lumen are 
 ciliated while the parenchymal cells are probably neuroglia. 
 
112 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 23. Cyclopterus lumpus. Cattle ('82). 60 In this form the 
 pineal organ is only rudimentary, being made up of a short, 
 conical body representing the stalk, while the distal part is 
 entirely absent. 
 
 24. Lota vulgaris. Cattie ('82). 60 As in Gadus, the end- 
 vesicle in this species lies against the roof of the skull. The cells 
 in this vesicle are similar to those in Gadus. 
 
 25. Pleuronectes platessa. Cattie ('82). 60 In this species the 
 stalk is solid and so also is the end- vesicle. The latter is highly 
 vascular and the stalk is very long. 
 
 26. Lucioperca vitrea. Hill ('94). 18 In this species the 
 anlagen of both the parapineal organ and the pineal organ 
 appear. 
 
 27. Lophius piscatorius. Studnicka ('96). 386 An end- vesicle 
 and a stalk are present in this form. The end-vesicle is in a 
 deep fossa. There are two types of cells in it besides the epen- 
 dymal layer, namely, neuroglia cells and sensory cells. Nerve 
 fibers were observed in the stalk. 
 
 28. Cepola rubescens. Studnicka ('96). 386 A thin stalk with 
 an expanded end-vesicle sharply flexed forward is the charac- 
 teristic in this species. The lumen in both is conspicuous. The 
 end- vesicle is much convoluted and rests against the roof of 
 the skull. 
 
 29. Anarrhichas lupus. Studnicka ('96). 386 In this form 
 there is a very long stalk, but no recognizable end- vesicle. There 
 is a tractus pinealis in the dorsal wall of the stalk and a plasmatic 
 lens in its lumen. 
 
 30. Ophidium barbatum. Studnicka ('96). 386 In this species 
 there is a thin, long, hollow stalk and a very small but elongated 
 end-vesicle. There is no fossa in the skull and no tractus 
 pinealis, but many blood vessels accompany the stalk as far as 
 the end-vesicle. 
 
 31. Arnoglossus lanterna. Studnicka ('96). 386 In this species 
 there is a hollow and long stalk with a well-marked end-vesicle. 
 This vesicle is vascular, but is situated in a position far removed 
 from the skull roof. 
 
THE PINEAL BODY 113 
 
 LOPHOBRANCHII 
 
 32. Syngnathus acus. Studnicka ('96). 386 The pineal organ 
 in this species is rudimentary, only the proximal portion of it 
 being present. In this there is a small lumen. 
 
 33. Hippocampus spinosus. Studnicka ('96). 386 The pineal 
 organ in this form is a small, short sprout, the distal end of which 
 does not reach the roof. 
 
 In all, thirty-three species of teleosts have been investigated. 
 Of these, thirty species present a more or less well-developed 
 pineal organ. In one form it is almost entirely absent present- 
 ing itself only as an inconspicuous rudiment. This is the case 
 in Syngnathus acus. In a second instance, Hippocampus 
 spinosus, the pineal organ is little more than a short sprout. In 
 five instances among the teleosts both pineal and parapineal 
 organs appear, the latter occurring either in the adult, which 
 is rare, or during the earlier stages of development. Both 
 organs appear in the anlagen in Coregonus albus, Lucioperca 
 vitrea, and Catostomus teres, but later disappear in these forms. 
 Both organs are well marked in anlagen and remain as discern- 
 ible rudiments in Salmo purpuratus and fario and also in Argyro- 
 pelecus hemigymnus. In one instance, Leuciscus cephalus, 
 there was definite evidence of secretory activity in the pineal 
 organ. In three species there was evidence of a retina in the 
 pineal organ, either because of the presence of specialized sensory 
 cells or of nerve fibers coming into connection with these cells. 
 In three instances there was a distinct parietal foramen. It is 
 significant in this connection to note that in no instance in 
 which there was a retinal-like structure or cellular formation 
 and arrangement suggestive of a retina, did there occur a parietal 
 foramen. In seven cases the end- vesicle of the pineal organ was 
 lodged in a fossa on the under surface of the skull. In seven 
 species, namely, Cobilis fossilis and barbatula, Lophius pisca- 
 torius, Cyprinus carpio, Carassius auratus, Anarrhichas lupus, 
 Pleuronectes platessa, and Clupea harengus, there is evidence 
 of a nervus pinealis or a tractus pinealis. All of these descrip- 
 tions except one are given by Studnicka. 386 This observer makes 
 the statement that there is no nervus pinealis in Ophidium 
 barbatum. 
 
 MEMOIR NO. 9 
 
114 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 5. Comparative anatomy and histology of the epiphyseal complex 
 
 in amphibia 
 
 In amphibia the pineal organ alone makes its appearance. 
 In no other form is this organ so little developed. It presents a 
 small end- vesicle which Stieda 379 first recognized and described 
 as the frontal subcutaneous gland. This end-vesicle is attached 
 by means of a thread-like strand to a considerably expanded 
 proximal portion, to which latter the name of epiphysis or corpus 
 pineale has been ascribed. The pineal organ consists, there- 
 
 Fig. 60 Head of Rana temporaria showing the unpaired pineal eye, situated 
 between the paired eyes, according to Stieda, 1865. 
 
 fore, of the usual parts, namely, an end-vesicle, a stalk, and a 
 proximal portion which is particularly conspicuous in amphibia. 
 The end-vesicle in so far as is known, is present in all forms 
 except Hyla arborea, the absence in this form being noted both 
 by deGraaf, 155 and Leydig. 238 In shape, the end-vesicle is round, 
 oval, or kidney-shaped. Stieda 379 and deGraaf 155 found it solid, 
 containing a lumen only in Bombinator. According to Stieda, 
 its diameters are from .12 to .15 mm. deGraaf found these 
 diameters in Rana esculenla from .126 to .145 mm., while 
 Lessona 241 in the forms studied by him found that the diameter 
 was less than 1 mm. A number of observers, including Ostrou- 
 moff 291 ('87) ; Leydig 238 ('91) ; Galeotti 140 ('96), and Braem 39 ('98), 
 
THE PINEAL BODY 
 
 115 
 
 maintain that the frontal organ contains a cavity. According 
 to Leydig, this organ contains pigment in Bombinator, but 
 otherwise, in frogs, the cells are pigment-free. Histologically, 
 the cellular elements of the frontal organ show no definite 
 arrangement. These cells are usually long and their mass 
 is traversed by a few isolated fibers. deGraaf and Leydig both 
 found evidence of fatty degeneration in the organ. The so- 
 called frontal subcutaneous gland of Stieda is situated, as de- 
 scribed by that author, directly under the corium of the skin 
 
 Epid 
 
 M 
 
 Pf V Ds Ch 
 
 Fig. 61 The epiphyseal complex in the pineal region of Rana temporaria, ac- 
 cording to Braem, 1898. 
 
 Ls., lamina terminalis; Pf., paraphysis; V., velum transversum; Ds., dorsal 
 sac; Po., pineal organ; N .pin., pineal nerve; Ch., commissura habenularis; Ep. t 
 proximal portion; Cp., posterior commissure; M.. midbrain. 
 
 in the midline of the head and upon a transverse line from pupil 
 to pupil. According to Lessona, 241 its position is marked by a 
 clear, white spot on the top of the head, not well developed in 
 all forms, but first described by Stieda 375 as the Scheitelfleck or 
 parietal spot. According to Leydig, 238 this spot is best made 
 out in Rana arvalis and agilis. It also occurs in Rana esculenta. 
 The stalk of the pineal organ in amphibia exists as a thin, 
 strand-like structure. Stieda 375 in 1865 first referred to it as 
 a thread connecting the frontal gland with the skull. Ciaccio 65 
 in 1867 recognized the nerve fibers in this strand. Lessona 241 in 
 1880, deGraaf 155 in 1886, and Leydig 238 in 1891, all observed the 
 nerve fasciculus in older animals, but did not appreciate its 
 significance. They thought it to be the remnant of the connect- 
 
116 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 ing strand between the attached and detached parts of the 
 pineal organ, thus representing a degenerative process. Braem 39 
 in 1898 also found this fasciculus and made the further observa- 
 tion that it contained heavily myelinized nerve fibers. He 
 likewise was of the opinion that there was evidence of degenera- 
 tion in this nerve fasciculus, in this way confirming the view of 
 deGraaf and Leydig. Haller 166 in 1898 stated that the fibers of 
 the tractus pinealis spring from two branches of roots connected 
 with the thalamus ventromedial to the commissura posterior. 
 Gaupp 147 in 1898, who first applied the term of tractus pinealis 
 to these fibers, observed fine nerve bundles passing in the ventral 
 portion of the epiphyseal stalk. Most observers believe that 
 these fibers come into relation with the posterior commissure. 
 The proximal portion of the pineal organ. This, as already 
 stated, was known as the epiphysis or corpus pineale. It was 
 also called by Gaupp 147 in 1898 the pediculus corporis pinealis. 
 Osborn 288 in 1884 described it as a cylindrical, hollow, anteriorly 
 flexed sac whose lumen was in communication with the third 
 ventricle. Rabl-Rtickhard 317 in 1880 states that the proximal 
 portion is solid. Osborn, on cross section, described it as 
 round. Gaupp 147 and Braem 39 state that the organ has an 
 elliptical form with many short diverticula which give it a 
 glandular appearance. In this feature it is like some teleosts, 
 reptiles, and birds. Galeotti 140 in 1896 found evidence of secre- 
 tory activity in Rufo and Rana, for example, granules in the 
 cytoplasm staining with acid fuchsin. Studnicka 386 in 1896 saw 
 the same appearances in adult animals which he thought were 
 sensory cells and which he likened to the sense cells in the pineal 
 organ in Petromyzon. Ostroumoff 291 in 1887 found fine fibers 
 between these cells. 
 
 Differences observed in the epiphyseal complex of the various 
 species of amphibia 
 
 URODELA 
 
 1. Amblysloma mexicanum. Stieda (75). 379 In this form the 
 chorioid plexus was first mistaken for the epiphysis. Orr 286 in 
 
THE PINEAL BODY 117 
 
 1889 first discovered the pineal organ in embryos. Eycles- 
 hymer 112 in 1892 made a more extensive study of this organ and 
 found the epiphysis to be a long, glove-finger shaped struct- 
 ure. The cells in the under wall were somewhat larger than 
 those in the upper wall and some of them contained pigment. 
 
 2. Amphiuma means. Osborn ('83). 287 In this species there 
 is a marked plexiform paraphysis, while the pineal organ extends 
 forward as a small sac over the commissura habenularis. 
 
 3. Menopoma alleghaniense. Osborn ('84). 288 The pineal 
 organ in this species is a saccular evagination with a lumen 
 opening into the third ventricle. 
 
 4. Menobranchus. Osborn ('84). 288 In this form the pineal 
 organ is a long, flattened sac completely detached from the 
 brain. Kingsbury 204 in 1895 showed that there is a well-marked 
 paraphysis and also that there are nerve fibers in connection 
 with the pineal organ. 
 
 5. Salamandra maculosa. Burckhardt ('91). 43 The pineal 
 organ in this species is a short, hollow, and rudimentary stalk. 
 There is a flattened end- vesicle in which there appears evidences 
 of degeneration. 
 
 6. Diemyctylus viridescens. Gage ('93). 135 The pineal organ 
 in this form is very small in the adult and there is no lumen in 
 any portion of it, There is, however, a well-developed para- 
 physis. 
 
 7. Desmognathus fuca. Fish ('95). 119 The pineal organ in 
 this species is a small compressed structure. It contains no 
 lumen in the adult, but in the larva the organ is hollow. 
 
 8. Triton taeniatus, cristatus and alpeslris. deGraaf ('86) 155 
 The pineal organ in these species is rudimentary. There is a 
 short, hollow stalk and a flattened end-sac in which there is 
 evidence of a process of degeneration. This same form was 
 studied by Blanc 34 in 1900 with practically the same results. 
 
 9. Spelerpes fuscus. Galeotti ('96). 14 In this species the 
 pineal organ is oval and hollow. The end-sac is directly in 
 connection with the commissura habenularis and there is no 
 stalk. The cells have an epithelial arrangement and are formed 
 in alveoli, giving the structure a glandular appearance. 
 
118 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 10. Proteus anguinus. Galeotti ('96). 14 The pineal organ 
 in this form is small and pyriform and has no evidence of 
 secretory function. 
 
 11. Salamandrina perspicillata. Galeotti ('96. 140 In this 
 species the pineal organ is a small, flattened structure. 
 
 APODA. 
 
 1. Ichthyophis gluiinosa. Burckhardt ('90). 42 The pineal organ 
 in this form is small and pyriform and has a short stalk, but 
 does not reach the skull roof. A well-developed paraphysis is 
 present. Fibers from the end- vesicle seem to make their way to 
 the commissura habenularis. 
 
 ANURA 
 
 1. Rana esculenta. Leydig ('68) , 233 In this species the end- 
 vesicle has a figure-of-eight shape and is solid. Leydig 238 later in 
 1891, could find no evidence of a parietal spot in Rana fusca. 
 deGraaf 155 in 1886 found a well marked end- vesicle which was 
 solid and round and a well-developed parietal spot. 
 
 2. Ceratophrys. Lessona ('80). 241 There is a fairly well- 
 marked end-vesicle in this species. 
 
 3. Bufo cinereus. Lessona ('80) 241 did not observe a pineal 
 organ in this form, but it was found subsequently by deGraaf 155 
 in 1886. Studnicka 386 also found it in young larvae. 
 
 4. Pelobates fuscus. Lessona ('80) 241 found the end- vesicle 
 in this species. 
 
 5. Discoglossus. Lessona ('80). 241 A fairly well-marked end- 
 vesicle exists in this species. 
 
 6. Alytes obstetricans. Lessona ('80) , 241 In this form there 
 is a well-marked end-vesicle which was first accurately described 
 by deGraaf. 155 
 
 7. Rana occipiialis and tigrina. Lessona ('80). 241 In these 
 forms the- pineal organ presents a well-marked end-vesicle. 
 
 8. Pipa americana. Lessona ('80). 241 In this species there 
 is no end- vesicle. 
 
 9. Hyla arborea. deGraaf ('86), 15 ' 5 and Leydig ('91) 238 both 
 found that the end-vesicle was absent and that the skin in the 
 usual position of the parietal spot showed nothing of the existence 
 of such a structure. 
 
THE PINEAL BODY 119 
 
 10. Bombinator igneus. Leydig ('68) ; 233 deGraaf ('86). 155 In 
 this species the end-vesicle is saccular. 
 
 In the twenty-two species of amphibia investigated, the great 
 majority present a well-developed paraphysis. In but a single 
 well-defined instance is there evidence of a tendency toward the 
 formation of a retina. This occurs in Amblystoma mexicanum 
 in which there is evidence of pigment formation in some of the 
 cells of the end-vesicle. In several forms the stalk contained 
 fibers suggestive of the pineal nerve. With reference to the 
 possible glandular character of the organ it must be borne in 
 mind that Stieda's 379 original description referred to the struc- 
 ture as the frontal subcutaneous gland. The general arrange- 
 ment of the cells, both in the end- vesicle and i(n the proximal 
 portion, has epithelial masses which tend to lend weight to the 
 view that the organ may have secretory function. In only one 
 instance, however, that is in Spelerpes fuscus, has there been 
 observed any definite evidence of glandular activity in the 
 pineal organ. 
 
 6. Comparative anatomy and histology of the epiphyseal complex 
 
 in Reptilia 
 
 In considering the conditions present in the epiphyseal com- 
 plex of reptilia, two groups of these animals must be distin- 
 guished. The first group is that comprising the more ancient 
 reptiles, e.g., the saurians and also the prosaurians as represented 
 by Sphenodon. In the second group are the reptiles of more 
 recent history, including ophidians, chelonians and crocodilians. 
 It is in the first group, however, that the most striking appear- 
 ances are observed in the epiphyseal complex. In these forms 
 there develops a structure so remarkable for the many features 
 which identify it as a visual organ that the term parietal or 
 third eye by which it has been designated seems altogether justi- 
 fied. Quite as striking in a negative way, on the other hand, 
 are the conditions in the ophidians and in the chelonians where 
 this eye not only altogether fails, but there is no evidence 
 whatever of a parapineal organ either in adult forms or in 
 the anlage, while the pineal organ also shows marked regressive 
 
120 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 alterations in the loss of several of its parts as compared with the 
 lower forms already considered. Finally the reported absence 
 of any epiphyseal structures whatsoever in crocodilia offers much 
 room for speculation or, perhaps, serves as an incentive to rein- 
 vest igat ion. 
 
 The pineal organ in saurians and prosaurians (form Sphenodori) 
 seldom presents all three of the several parts usually observed 
 in the pineal organ, and it is not possible to identify an end- 
 
 Schd 
 
 Fig. 62 The epiphyseal complex in Sphenodon according to Spencer, 1886. 
 Pa., parapineal organ (end-vesicle); Pf., paraphysis; Ds., dorsal sac; Ep., 
 fproximal portion of pineal organ; M., midbrain. 
 
 vesicle, a stalk, or a proximal portion. Often the end- vesicle is 
 absent, and in no instance does it assume the proportions or 
 the characteristics of a visual organ. The stalk is usually 
 hollow, but contains no nerve fibers, and in the instances in which 
 the end- vesicle is absent, the stalk is drawn out into a tapering 
 process or end-tube. Melchers 269 in 1899 showed that not only 
 may the end-sac be absent, but the rest of the parapineal organ 
 may present itself in a degenerative condition. This is true in 
 
THE PINEAL BODY 121 
 
 Platydactylus. In some cases, as in Gehyra oceanica and 
 Hemidaclylus mahouia, described by Stemmler 374 in 1900, the 
 entire epiphyseal complex may be only recognized in the slightest 
 rudiment possible. In one instance reported by Studnicka, 386 
 namely, Pseudopus pallasi, there is an end-vesicle, a stalk, and 
 & proximal portion. The stalk is, in fact, a double one, or, in 
 other words, there is a main stalk and a secondary accessory 
 connection between the end-vesicle and the roof-plate of the 
 brain. 
 
 The proximal portion of the pineal organ, known as the epi- 
 physis or corpus pineale, is present in all forms. In some cases 
 the proximal portion is a simple pyriform structure attached by 
 a thin stalk to the roof of the interbrain. In other instances it 
 is spindle-shaped or oval. The walls of the proximal portion 
 are thick and usually flat inside as well as outside. In some 
 cases there are inner reduplications, as in the fish. Leydig 238 
 in 1891 found thick accessory spaces in the organ of Lactera 
 ocellaia and Anguis fragilis due to septal formation. The wall 
 may be much folded, giving the appearance of a complicated 
 glandular structure. Edinger 105 in 1890 showed this in one of 
 his cuts (fig. 63). 
 
 The histological structure of the pineal organ. The chief cellular 
 constituent of the pineal organ, both in its end-vesicle when 
 present and in the proximal portion, is the ependymal cell. 
 Neuroglia cells also occur interspersed among the ependymal 
 elements, but there are no ganglionic cells. Nerve fibers lie 
 parallel with the outer dorsal surface quite similar to the nerve 
 fibers in other pineal organs. These are probably the nerve 
 fibers which constitute the tractus pinealis. Klinckowstroem 207 
 in 1893 found cilia on the cells of the pineal organ in embryos 
 of Iguana and Tejus, but not in the adults of these species. 
 Pigmentation is either entirely absent in all parts of the pineal 
 organ or when present it is in the interior of the cylindrical 
 cells placed in the lumen. A tractus pinealis was described by 
 Leydig 239 in 1896 in Platydactylus. Melchers, however, 269 in 1899, 
 showed these fibers were probably connective tissue. Saurians, 
 .as a rule, although they do not in every case present a well- 
 
122 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 marked tractus pinealis, nevertheless in a certain number of 
 instances a nerve tract may be observed connecting the pineal 
 organ with the roof of the interbrain. 
 
 In Ophidia the pineal organ is rudimentary. Only the prox- 
 imal portion persists in the snakes. This, however, has under- 
 gone considerable modification from the proximal portion already 
 encountered in the lower vertebrates. In the true snakes it is 
 a compact, highly vascular structure to which the term epiphysis 
 or corpus pineale may, in the strict sense, be applied. Hoff- 
 
 Epid 
 
 Pa 
 
 Fig. 63 The epiphyseal complex in Anguis fragilis, according to Leydig, 
 1891. 
 
 P. a., parapineal organ; Ep., proximal portion of pineal organ. 
 
 mann 186 in 1886 showed that the corpus pineale in ophidia begins 
 in its development as a simple evagination from the interbrain 
 roof. How it attains its later complicated, compact form is not 
 yet exactly known. No doubt the solid epiphysis due to the 
 proliferation of the wall of the anlage causes the obliteration of 
 the lumen of the original evagination. A paraphysis develops 
 early in ophidians and has in its inception the same general form 
 as the epiphysis. The pineal region in the adult consists, there- 
 fore, of a paraphysis which is a thick-walled structure associated 
 with the chorioid plexus, a velum transversum and a dorsal sac 
 
THE PINEAL BODY 123 
 
 also complicated in the chorioid plexus, a commissura habenularis, 
 an epiphysis with a fairly well marked recessus pinealis and a 
 posterior commissure. Herrick 177 in 1891 described the epi- 
 physis in ophidia as a compact, somewhat rounded or oval 
 body whose interior consists of a connective tissue network with 
 many blood vessels, thus giving it the appearance of a branched, 
 tubular gland. Studnicka 386 maintains that nothing definite is 
 known of the significance of the epiphysis in snakes. Its un- 
 usually rich capillary blood supply speaks in favor of the sup- 
 position that the organ is a gland which contributes its product 
 to the blood stream. 
 
 In Chelonia the pineal organ is only in a rudimentary condi- 
 tion and develops in these forms an epiphysis or corpus pineale. 
 Just as in ophidians, the end-vesicle and the stalk of the pineal 
 organ appear not to be laid down in anlage, or if it does occur in 
 the early stages of the development, it soon disappears, leaving 
 only the proximal portion to represent the pineal organ in these 
 forms. Neither in chelonia nor in ophidia is there any evidence 
 of an anterior epiphysis, that is to say, a parietal eye. The 
 first description of turtles was given by Bojanus 36 in 1819. 
 Tiedemann 395 also mentioned the epiphysis in turtles, but prob- 
 ably mistook the chorioid plexus for that structure. Voeltz- 
 kow 410 in 1903, describing the embryology of Chelone imbricata, 
 mentions the first appearance of the epiphysis as a simple evagi- 
 nation. Secondarily, a stalk develops between the pineal organ 
 and the roof of the interbrain, so that, according to Voeltzkow, 
 the epiphysis in Chelone imbricata separates itself entirely from 
 the roof-plate. The pineal region in chelonia presents the 
 usual features, namely, a large paraphysis which forms an 
 unusually extensive sac. The end of this sac lies directly over 
 the epiphysis. The velum transversum and dorsal sac are 
 incorporated in the chorioid plexus. There is a fairly well 
 marked commissura habenularis, the epiphysis in its usual 
 chelonial form, and also the posterior commissure. The form 
 of the epiphysis in the turtle is oval or ovoid; it lies close to 
 the roof-plate. The surface, as Herrick 177 has shown in 1891, 
 is uneven and may indicate r, process of lobulation. Many 
 
124 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 trabeculae of connective tissue extend inward toward the center 
 of the organ from the capsule. The cellular elements are for 
 the most part ependymal cells and neuroglia. No ganglionic 
 cells and no nerve fibers were observed. There is no clear 
 evidence of secretory function in the epiphysis of Chelonia. The 
 organ contains a small cavity. 
 
 In Crocodilia, the pineal organ, according to Sorensen ('94) , 363 
 as well as the other elements of the epiphyseal complex, is en- 
 tirely absent. In the roof of the interbrain there is a well 
 marked commissura habenularis and a posterior commissure 
 with possibly a dorsal sac and a paraphysis. Voeltzkow 410 in 
 1903 found no epiphysis in Crocodilus madagascariensis. Rabl- 
 Rtickhard 316 in 1878 showed in Alligator mississippiensis a 
 long, rounded conarium. This observation, according to later 
 observers, is probably an error, the paraphysis and chorioid 
 plexus having been mistaken for the pineal body. 
 
 The parietal eye in Reptilia. The parapineal element in 
 saurians and sphenodon gives rise to what is known as the 
 third or parietal eye of reptiles. Among the saurians it is not 
 universally present. Its absence has been noted in certain of 
 the Geckonidae, as for example, Hemidactylus, Gehyra, Gecko, 
 and Platydactylus. It is also absent in certain Agamidae, such 
 as Draco, Ceratophora, Lyriocephalus, and Moloch. It has not 
 been observed in Tejus and Cyclodus. The general form of the 
 parietal eye is saccular with the upper wall corresponding to a 
 lens which is pigment free while the under or ventral wall which 
 corresponds to the retina is deeply pigmented. The third eye 
 presents several different forms in the different species: 
 
 1. It may be pyriform, as is the case in Sphenodon, Spencer 366 
 and Ley dig, 236 and Iguana, Spencer. 367 It is also of this shape in 
 Varanus nebulosus and Anguis, Hanitsch, 169 also in Pseudopus 
 pallasi, Studnicka. 386 
 
 2. Dorsoventrally elongated and ovoid as in Anolis and 
 Lyriocephalus, Spencer. 367 
 
 3. Spherical or hemispherical, in which latter case the lens is 
 flattened, as in Lacerta ocellata, Chameleon, Grammatophora 
 barbata, Moloch horridus, and Agama hispida, Ley dig 238 and 
 Spencer. 368 
 
THE PINEAL BODY 
 
 125 
 
 4. Lenticular and flattened, as in Anguis frcgilis, Lacerta 
 vivipara, Lacerta agilis, Lacerta viridis, Seps tridactylus, Varanus 
 giganteus, Plica, Iguana, and Calotes. 
 
 5. Flattened so that the under wall is pressed inward, 
 as in Varanus bengalensis, Leiolaemus nitidus, and Calotes 
 ophiomachus. 
 
 6. Flattened and decidedly elongated, as in Seps chalcidica 
 and Calotes versicolor. 
 
 Fig. 64 The pineal eye of Anolis, according to Spencer, 1886 
 
 While the dorsal wall of the parapineal vesicle forms the true 
 lens of the parietal eye, the ventral wall is pigmented and gives 
 rise to the retina. The latter consists of layers of different 
 types of cells. In the embryonic stages it is attached to the 
 brain by a tubular prolongation from the roof-plate. The first 
 detailed description of the parietal or third eye in reptiles was 
 given by deGraaf 155 in 1886. Spencer's 366 work appeared in 
 the same year, and a number of investigations have been reported 
 since then confirming in a general way the conclusions of these 
 
126 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 early workers. These researches include those of Beraneck 
 ('87) 21 in Anguis and Lacerta; Francotte ('87) 127 in Anguis; 
 McKay ('88) 255 in Grammatophora and Hinulia; Strahl and 
 Martin ( J 88) 383 in Lacerta, and Ritter ('91) 332 in Phrynosoma. 
 There is a general agreement regarding the histological structure 
 of the retina among saurians, and the following layers have 
 been identified by most of the investigators mentioned : 
 
 Fig. 65 The structure of the retina in the pineal eye in Sphenodon punctatum, 
 according to Spencer, 1886. 
 
 1. An inner layer of long, cylindrical cells, called the rods or 
 rod-like bodies of Spencer 366 or the cellules batonnets of Fran- 
 cotte. 127 In these cells pigment occurs. 
 
 2. An inner layer of cells, called the 'couche cellulaire interne' 
 by Francotte. 127 This consists of round cells with a large round 
 nuclei. Ritter 332 distinguishes two types of nuclei in this layer, 
 namely, those which are round and small and those which are 
 oval and long. 
 
THE PINEAL BODY 
 
 127 
 
 3. A molecular layer described by Spencer 366 and Francotte 127 
 or a layer of nerve fibers described by Strahl and Martin. 383 
 The latter observers and Klinckowstroem 206 maintain that these 
 fibers are in connection with the parietal nerve. Leydig 238 and 
 Dendy 86 believed that a cleft occurred in this layer which, ac- 
 cording to Leydig, gives rise to a lymph space. 
 
 4. An outer cellular layer of round cells somewhat deeper than 
 the second layer. 
 
 5. A membrana limitans externa. 
 
 Fig. 66 The pineal eye in Iguana tuberculata, according to Klinckowstroem, 
 1894. 
 
 The most important elements in the retina are the rod cells 
 which appear to correspond to the ependymal cells of the retina 
 in the pineal organ of Petromyzon. They are long, cylindrical 
 elements in which may be differentiated an outer thread-like 
 part and a more cylindrical portion. The nucleus occupies an 
 enlargement in the area of transition between these two por- 
 tions. The inner cylindrical parts lie close together; the outer 
 thread-like parts have broad spaces between them in which 
 are lodged neuroglia and some ganglionic cells. The peripheral 
 processes come to the surface of the retina and spread out against 
 
128 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 the membrana limitans externa. The pigment in the cells is in- 
 some cases arranged in transverse bands or stripes, according 
 to Spencer 366 in Sphenodon and Ley dig ('9 1), 238 in Anguis. All 
 of the rod cells are similar. The connection of the retinal ele- 
 ments with fibers of the parietal nerve is not yet altogether 
 understood. In adults the organ is rudimentary. It is not 
 known whether the nerve fibers come from the large retinal 
 elements, from the ganglionic cells of the deep retinal layer, or 
 from the large cylindrical cells of the inner layer. The latter 
 seems most probable in view of the conditions in Petromyzon. 
 
 The parietal nerve. This nerve was first described by Spencer 366 
 in 1886 and has been observed by many others since then. 
 Spencer believes that the parietal nerve is connected with the 
 end of the epiphysis, that is to say, a direct continuation of the 
 pineal organ. The entire course of the parietal nerve from the 
 parietal eye to the brain roof was first traced by Strahl and 
 Martin 383 in 1888 in older embryos of Lacerta vivipara and 
 A nguis fragilis. These observers showed that the nerve was 
 completely independent of the epiphysis. Beraneck 23 in 1892 
 made more exact studies and confirmed the view of Strahl and 
 Martin. Other authors are also emphatic in stating the com- 
 plete independence between the epiphysis and the parietal eye. 
 Among them are Studnicka ('93), 384 in Lacerta; Klinckowstroem 
 ('94) 209 in Iguana; Leydig ( J 96) 239 and Bendy ( 7 99) 87 in Spheno- 
 don, and Schauinsland ('03) 347A also in Sphenodon. The parietal 
 nerve begins to develop shortly after the separation from the 
 roof of the parietal eye. Of the direction of its fibers, whether 
 from the brain to the eye or, as is the case in the pineal organ 
 and the paired eyes, from the eye to the brain, there is no proof. 
 The latter course, however, is most probable. In Anguis, the 
 parietal nerve first appears at 50 mni. embryo size and reaches 
 its maximum of development between the 27 and 30 mm. size. 
 In Iguana, the nerve is well developed at fourteen days and is 
 at its maximum at twenty-four to twenty-six days. Between 
 the thirtieth and fortieth days it shows signs of reduction. 
 Strahl and Martin 383 showed that the nerve comes into relation 
 with the ganglionic cells forming a prominence with the brain 
 
THE PINEAL BODY 
 
 129 
 
 roof. This Beraneck 23 designated in 1892 as the noyau parietal. 
 The prominence thus described can be nothing else than the 
 closely set ganglia habenulae of the interbrain as shown by 
 Studnicka 384 in 1893 in Lacerta, by Klinckowstroem 209 in 1894 
 in Iguana, and by Leydig 239 in 1896 in Lacena. The parietal 
 nerve is made up of fine fibrils; it has a perineurium, a connec- 
 
 * ; 
 
 Fig. 67 The pineal eye of Varanus giganteus, according to Spencer, 1886. 
 Pa., parapineal organ; Npar., parapineai nerve; Bl., blood vessel. 
 
 tive tissue, and glial sheaths. In Iguana it degenerates and 
 disappears in the adults, according to Klinckowstroem ('94). 20<J 
 In some cases Spencer 366 found the parietal nerve divided into 
 two or three strands, for example, in Lacerta ocellata and 
 Varanus gigameus. A similar splitting was found by Studnicka 384 
 in 1893 in Petromyzon. Klinckowstroem 209 in Iguana recognized 
 a second parietal nerve which arose from the left habenular 
 
 MEMOIR NO. 9 
 
130 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 ganglion and passed close behind the first nerve to the parietal 
 eye. The lens of the parietal eye is not uniform in its shape; 
 it occurs in the following different forms: 
 
 1. Regular bi-concave lens, both surfaces curved, which is 
 most common in Lacerta vivipara, Lacerta agilis and Lacerta 
 ocellata, Leiolaemus nitidus, Seps chalcidica, Phrynosoma doug- 
 lassi, and Sphenodon. 
 
 2. Bi-convex, with the under surface more convexed than the 
 upper, as in Anolis and Sphenodon. 
 
 3. Plano-convex, as in Anguis and Iguana. 
 
 4. Concavo-convex, as in Calotes, Varanus bengalensis, and 
 Varanus giganteus. 
 
 The structure of the lens is made up of peculiar, long, cylin- 
 drical cells apparently derived from modified ependymal cells. 
 These are the so-called lens cells. There are some intercellular 
 spaces, probably lymph spaces, according to Leydig ('91). 238 
 The lens cells are nearly free of pigment. The substance of these 
 cells is very hard. Their nuclei are oval or round and are sel- 
 dom scattered over the entire lens surface or its entire thick- 
 ness. They are most numerous at the border of 'the lens where 
 the latter passes over into the retina. 
 
 The parietal foramen. Leydig 234 in 1872 found a round or oval 
 opening in the skull of Sphenodon situated in the osparietal, 
 which seemed either directly to serve as the outlet for the parietal 
 organ or else for the entrance of light rays. It was reminiscent 
 of a similar opening in the cartilaginous roof of the cranium in 
 selachians. In most cases the parietal eye is in, or directly 
 under, this foramen. Species which do not possess a parietal 
 eye have a parietal foramen which is filled by the pineal organ, 
 in which case, the end-vesicle takes the place of a third eye as 
 far as location is concerned. The foramen is absent in a large 
 number of saurians, particularly in the Geckonidae, and it is 
 also absent in Ceratophora aspera. There are also instances in 
 which the foramen does actually appear in some individuals of a 
 species and yet in other individuals of the same species it is closed 
 by bone. The eye usually lies in the middle of this foramen or 
 near its upper edge. The relation between eye and foramen is 
 
THE PINEAL BODY 131 
 
 different in different periods of life. The foramen is not the 
 result of direct pressure of the eye, but occurs for the purpose of 
 permitting the passage of light rays. As a rule, the parietal eye 
 lies in the foramen or under it, so that its optic axis corresponds 
 to that of the foramen. In Sphenodon a single exception to 
 this rule is noted by Spencer. 366 Here the organ is tipped for- 
 ward so that the light rays cannot reach the entire retina. The 
 size of the foramen differs and bears no direct relation to the 
 size of the parietal eye. The third eye is connected to the 
 foramen by means of connective tissue and is surrounded by 
 lymph spaces while blood vessels make up a net about the 
 edges of the foramen. No mention of muscular tissue or dis- 
 crete muscles has been made in connection with the parietal 
 eye. 
 
 Ley dig 238 in 1891 found in Lacerta muralis, near the tip of 
 the epiphysis, four round, free, calcium bodies. Similarly in 
 Varanus nebulosus many small pieces of calcium carbonate have 
 been observed. These, however, have nothing to do with the 
 more common deposits of brain sand in the pineal organ of 
 mammals, as Ley dig 238 originally thought. 
 
 The interior of the parietal eye contains a coagulum, the 
 vitreous or the corpus vitreum. This consists of a syncytial 
 layer of cells entirely free of pigment. A sclera has been de- 
 scribed as developing in connection with the membrana limitans 
 externa which passes over into the connective-tissue sheath of 
 the eye. There is a space between these two layers which was 
 originally supposed by Ley dig 238 to be a large lymph space. In 
 most cases the connective tissue forms a sheath for the eye 
 which may be considered as a sclera. In other instances it is 
 absent. The connective-tissue capsule of the parietal eye is 
 considered analogous to the sheath of the eye in Petromyzon. 
 The connective tissue above the eye becomes differentiated as a 
 cornea and contains no pigment. It is almost fiberless connective 
 tissue. A parietal spot is absent in those saurians in which 
 no parietal eye or no parietal foramen develops. It is recognized 
 as a less pigmented area in the skin and presents many different 
 appearances, as well as differences in size, in the several species 
 of saurians (fig. 68). 
 
132 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Accessory pineal and parapineal organs in Reptilia. A number 
 of observers have reported the appearance of accessory struc- 
 tures in connection with both the pineal and parapineal organs. 
 Such observations have been made by Spencer ('86) 366 in Plica 
 umbra; by Duval and Kalt ('89)" in Anguisfragilis; by Carriere 57 
 in 1890; by Prenant 311 in 1893-94-96; by Leydig 237 in 1890-91, 
 and by Francotte 130 in 1896. Accessory organs were also found 
 
 Fig. 68 The corneal scale in Calotes, according to Spencer, 1886 
 
 in Laceria vivipara by Burckhardt 46 in 1894; by Francotte 130 in 
 1896; by Klinckowstroem ('94) 209 in Iguana, and by Studnicka 
 ('93) 384 in Pseudopus pallasi. Accessory epiphyseal organs may 
 arise either from the lateral wall of the end- vesicle of the pineal 
 organ or the under wall of the parietal eye. There are two 
 types of accessory organs: 1) accessory pineal organs, and 2) 
 accessory parietal eye organs. The following are the possibili- 
 ties for accessory pineal organs : 
 
THE PINEAL BODY 133 
 
 1. Evaginations of the distal end of the epiphysis as in Anguis 
 and Iguana. 
 
 2. Independent buds off the epiphysis or extrusions from 
 it held in relation by pigment strands of cells, as in Lacerta 
 vivipara. 
 
 3. Isolated extrusions from the end of the epiphysis. 
 Accessory parietal eye organs are less common. Carriere 57 
 
 in 1890 showed a diverticulum from the under wall of the parietal 
 eye. Prenant 312 in 1895 made the same observation. Fran- 
 cotte 127 found that these accessories consist of a lens and retina 
 which are still in connection with the chief organ. Accessory 
 organs usually have pigment in them, but this is not so in Phry- 
 nosoma and Sphenodon. Only the under wall is pigmented as 
 a rule, so that the under wall corresponds to the retina while 
 the upper wall corresponds to the lens. Such accessory organs 
 attached to the parietal eye indicate an attempt to produce 
 another optic organ. Only exceptionally does the upper or 
 dorsal wall show a lens formation. In Pseudopus, Studnicka 384 
 in 1893 found that the interior of the accessory parietal eye con- 
 tained a syncytium as does the actual parietal eye. Prenant 312 
 in 1895 differentiated the following types of accessory organs in 
 Anguis: 
 
 1. Epiphyseal eye. This lies close to the epiphysis, yet sepa- 
 rated from it and is entirely derived from that organ. 
 
 2. Interparietal-epiphyseal eye. This is situated in the mid- 
 line between the epiphysis and the parietal eye. It is the most 
 frequent of the accessory parietal eye organs. 
 
 3. Intraparietal eye. This is connected with the retina and 
 under wall of the parietal eye or else is included in it. 
 
 4. Accessory chorioidal eye. This is found very infrequently. 
 It is widely separated from both parietal organs and presents 
 itself as a pigmented hollow vesicle lying on the upper surface 
 of the chorioid plexus. 
 
 Accessory parietal organ structures are most frequent in 
 embryos and tend to disappear in the adult. This observation 
 is agreed to by most authors. 
 
134 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Differences observed in the epiphyseal complex in the various 
 
 species of reptiles already investigated. 
 PROSAURIANS 
 
 1. Sphenodon punctatum (Hatteria). Spencer ('86) ; 367 Leydig 
 ('91) ; 238 Hoffmann ('90) ; 187 Dendy ('99) 87 described a develop- 
 ment, as did also Schauinsland 346 in 1899 and 1903. 
 
 The pineal organ in the embryo is a simple evagination with a 
 thin stalk which is solid. The walls of the end-vesicle have 
 many folds. Only the cells in the interior retain a brown pig- 
 ment. The parietal nerve, according to Spencer, is a prolonga- 
 tion from the end of the epiphysis. Such a connection does 
 exist in some adults, but is of a connective tissue character. 
 Dendy and Schauinsland identified the actual parietal nerve. 
 It arises in front of the epiphysis and is independent of it. The 
 parietal eye is conical or pyriform in shape and the retina and 
 lens are both well developed. In older embryos the nerve 
 does not enter the middle, but rather comes into relation with 
 the posterior third of the eye. The structure of the retina 
 was most minutely described by Spencer, Leydig, and Dendy. 
 It has rod cells and several other layers of cells. It contains 
 pigment as well as a molecular layer and a layer of large gan- 
 glionic cells. The lens is bi-convex. The entire organ is sur- 
 rounded by a connective tissue capsule. Dendy mentions a 
 thin-walled sac in the embryo between the epiphysis and para- 
 physis. This undoubtedly is an accessory organ. Sphenodon 
 has a parietal foramen and a superficial apparatus usually con- 
 nected with the parietal eye. 
 
 SATJRIANS LACERTILIA VERA. 
 
 GECKONIDAE. 1. Gecko ver us. Spencer ('86). 367 In this spe- 
 cies only the epiphysis is present. There is no parietal foramen 
 and no parietal spot. 
 
 2. Platydactylus muralis. Spencer ('86) ; 367 Leydig ('91) ; 238 
 Melchers ('99). 269 In this form there is no parietal eye, the 
 epiphysis being the only element to appear. This latter con- 
 sists of an end-vesicle which is large and thick-walled having 
 no folds; its stalk is short and solid. The entire pineal organ is 
 
THE PINEAL BODY 135 
 
 flask-shaped. There are many intercellular spaces in the end- 
 vesicle. These same observations hold good for Mauritanicus. 
 
 3. Hemidaclylus verruculatus. Leydig ('91). 238 This species 
 possesses no parietal eye. There is an end-vesicle which con- 
 tains a brown pigment. The vesicle is drawn out into a small 
 point. 
 
 4. Hemidactylus mabouia. Stemmler ('00). 374 In this form 
 the pineal organ only is present and the end- vesicle is an atten- 
 uated bud. The proximal portion of the stalk is solid. There 
 is no pigment and no fibers in connection with the organ. 
 
 5. Gehyra oceanica. Stemmler ('00). 374 The parietal eye is 
 not well developed. The pineal organ alone makes its appear- 
 ance and has a definite end-vesicle. The stalk has a lumen in 
 its proximal portion. The cells in the end-vesicle are ependymal 
 in type. There are no folds in the wall. 
 
 AGAMIDAE. 1. Draco volans. Spencer ('86) ; 367 Studnicka 
 ('93). 384 There is no parietal eye in this species. The pineal 
 organ is a broad, dorsoventrally compressed end-vesicle con- 
 taining no pigment. 
 
 2. Ceratophora aspera. Spencer ('86). 367 In this form there 
 is no parietal eye. An end-vesicle develops, but there is no 
 parietal foramen. 
 
 3. Lyriocephalus scuiatus. Spencer ('86). 367 There is no 
 parietal eye in this species. An end-vesicle exists with an 
 attenuated stalk. There is no pigment, but the animal has a 
 definite parietal spot. 
 
 4. Calotes ophiomachus and versicolor. Spencer ('86). 367 The 
 epiphysis ends at the edge of the parietal foramen. The 
 parietal eye is present. Spencer saw only rods in the retina. 
 The lens is concavo-convex. Some of the lens cells and retinal 
 cells are pigmented. A well-marked parietal foramen is present 
 and there is a small modified cornea with parietal spots. 
 
 5. Agdma hispida. Spencer ('86). 367 This species has a 
 parietal eye, a retina, lens, and a parietal foramen, together 
 with a cornea and parietal spot. 
 
 6. Grammatophora barbata. Spencer ('86). 367 In this form 
 there was found some evidence of a parietal eye, the under 
 
136 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 wall of which was definitely pigmented. McKay ('88) 255 found 
 a bi-convexed lens, a go'od retina with rod cells and round cells, 
 a molecular layer, and also a spindle-celled layer and peculiar, 
 triangular elements. The lumen was traversed by a fine strand. 
 
 7. Moloch horridus. Spencer ('86). 367 In this species the 
 organ is strongly pigmented, more likely an end-vesicle with a 
 stalk than a parietal eye. The parietal foramen in which the 
 organ rests is present. Both cornea and parietal spot are 
 present. 
 
 8. Agama caucasica. Owsiannikow ('88). 295 In this species 
 there is a relatively large parietal eye with rods in the retina, 
 which latter is otherwise well developed, There is also a lens, 
 a parietal foramen, a vitreous, cornea, and a parietal spot. In 
 one case, Ritter ('94) 333 found an accessory organ which he 
 called the parapineal organ. It was situated in the parietal 
 foramen somewhat to the left of the parietal eye. No corium 
 was above it. A common, connective tissue capsule contained 
 both organs. The accessory organ was larger than the parietal 
 eye. There was no lens or retina in the accessory organ. 
 
 9. Phrynocephalus Vlangalii. Owsiannikow ('88). 295 In the 
 20 mm. embryo this species has a parietal eye. The organ is 
 deeply pigmented. 
 
 IGUANIDAE. 1. Phrynosoma orbiculare. Studnicka ('93). 384 
 In this species the epiphysis is broad and globular and con- 
 nected by a stalk to the roof of the brain. It presents an end- 
 bud on its distal extremity. Ependymal cells in the body con- 
 tain a brown pigment. In the lumen there is a coagulum which 
 consists of a syncytium of pigment-containing cells. The pari- 
 etal nerve was not observed. The parietal eye is small, dorso- 
 ventrally flattened with a well-developed lens and retina. The 
 lens is bi-convex. The cells of the lens have their nuclei situated 
 near the under surface. The retina is filled with pigment, hid- 
 ing its main structure. The position of the parietal eye is in a 
 wide foramen, four times as large as the parietal eye itself. The 
 parietal cornea and spot are present. 
 
 2. Anolis. Spencer ('86). 367 This species presents a well-devel- 
 oped parietal eye which is ovoid in form and has a well-developed, 
 
THE PINEAL BODY 137 
 
 thick retina. The latter is pigmented and contains rod cells. 
 The lens is bi-convex. What Spencer considered a nerve was in 
 all probability connective-tissue remains of a former nerve. A 
 narrow parietal foramen occurs while the cornea and parietal 
 spot are absent. 
 
 3. Leiolcemus niiidus. Spencer ('86). 367 In this form the 
 epiphysis exists as a hollow, proximal part and a horizontal 
 solid end portion. The latter is stretched forward to reac the 
 parietal foramen. The parietal eye is dorsoventrally flattened 
 and has a narrow lumen. The upper surface of the retina is 
 flat and horizontal. The lens is present. There are rod cells 
 which are the chief elements in the retina. The lens is bi- 
 convex and the nuclei of the lens cells lie in a layer deeply 
 situated. There is a parietal foramen in which the eye is lodged. 
 The corium is clear. There is a light colored parietal spot. 
 
 4. Leiolaemus tennis. Spencer ('86). 367 The epiphysis ex- 
 tends forward to a well-marked parietal eye. There is no con- 
 nection between the two. The parietal eye has a pigmented 
 retina and a lens. The parietal cornea and parietal spot are 
 present. 
 
 5. Plica umbra. Spencer ('86). 367 The epiphysis has , a prox- 
 imal part and a horizontal portion which is solid and reaches the 
 parietal eye. The latter is connected with the epiphyseal end- 
 sac. The parietal eye is much flattened and the retina is pig- 
 mented. It is situated in a deep parietal foramen. The cornea 
 is present as well as the parietal spot. 
 
 6. Iguana tuberculata. Spencer ('86) ; 367 Leydig ('96) ; 239 
 Klinckowstroem ('93). 207 In this form the epiphysis is well 
 developed with a large end-bud in connection with the proximal 
 portion. The latter has a more or less follicular appearance. 
 In embryos the cells have cilia, but these later disappear. Klinc- 
 kowstroem in the 18 mm. embryo describes a tractus pinealis in 
 the distal end of the epiphysis. A parietal nerve is described by 
 the same author in 1894. In embryonic stages it connects the 
 retina with the roof of the brain. The parietal eye is globular 
 and in some forms a highly differentiated retina is present. An 
 actual nerve layer appears only in the embryo and later disap- 
 
138 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 pears. The pigment increases in the older animals. The lens 
 is plano-concave. The eye rests in a parietal foramen. The 
 cornea is present as well as a marked parietal spot. 
 
 7. Phrynosoma douglassi. Ritter ('91). 332 There is an epi- 
 physeal vesicle in this form and a posteriorly flattened vesicle 
 which contains no lumen. It is connected by a very thin stalk 
 to the epiphysis. The parietal eye is connected with the brain 
 roof and is a laterally compressed vesicle. The lens and retina 
 are both well developed. The retina has an outer cell layer, a 
 molecular layer, and an inner layer with two elements, one round 
 and the other elongated, and finally an inner layer of rod cells. 
 There is a coagulum in the cavity of the eye vesicle. The lens 
 is slightly bi-convex. The nuclei of the lens cells lie near the 
 inner periphery of the lens. The position of the eye is in a 
 broad foramen. The parietal cornea and pit, as well as a pari- 
 ietal spot, are all present. 
 
 8. Uta stansburiana. Ritter ('91) ; 332 Studnicka ('95). 386 The 
 parietal eye in this form is also ventrally flattened. The lens is 
 separated from the retina. There is deep pigment in the retina 
 and the eye rests in a parietal foramen. 
 
 9. Sceleporus undulatus. Herrick ('9 1) 178 in describing the 
 epiphysis in this form, states that the .under wall has some 
 similarity to the retina. 
 
 10. Phrynosoma coronatum. Ritter ('91) ; 332 Sorensen ('93). 361 
 The epiphysis is similar to that in Phrynosoma douglassi. It is a 
 thick-walled vesicle. The cells in the interior are deeply pig- 
 mented. There is a connective-tissue strand running to the 
 parietal eye. The parietal nerve extends from the commissura 
 posterior to the parietal eye. The eye is not as well differ- 
 entiated as in Phrynosoma douglassi, although it is present. 
 
 11. Sceleporus striatus. Sorensen ('94). 363 In this form the 
 epiphysis is attached to the roof by a thin, peculiarly white 
 stalk. The parietal nerve presents no peculiarities, but arises 
 from the anterior portion of the commissura habenularis. It is 
 solid to the extreme end of the epiphysis where it proceeds to 
 the parietal eye, the latter apparently being independent of the 
 end of the epiphysis. No parietal foramen is present. The 
 
THE PINEAL BODY 139 
 
 parietal eye has the form of a dorsoventrally compressed sac 
 which has a lens and well-marked retina, the latter has a double 
 layer of well-pigment ed cells. Rod cells also are present. The 
 entire parietal organ is enclosed in a connective-tissue capsule. 
 
 ANGUIDAE. 1. Anguis fragilis. Leydig ('96) ; 239 deGraaf 
 ('86) ; 155 Spencer (86) ; 368 Beraneck ('92) ; 23 Hanitsch ('88); 169A 
 Strahl and Martin ('88) ; 383 Francotte ('96) ; 130 Owsiannikow 
 ('88) ; 295 Duval and Kalt ('89;) 99 Carriere ('90) ; 57 Prenant, 
 ('95) , 312 and Studnicka ('93). 384 
 
 The epiphysis in this species consists of a proximal and a 
 distal portion. The end portion of the epiphysis is deeply 
 pigmented. The parietal eye is connected by a connective- 
 tissue strand to the epiphysis. The parietal nerve is present 
 only in embryos and arises from the ganglion habenulae. The 
 parietal eye is lenticular in form, dorsoventrally flattened, and 
 has a deeply pigmented retina. The lens is bi-convex and plano- 
 convex. The lumen contains a coagulated substance with a 
 syncytium. There is a well-developed capsule. Accessory 
 organs are common. The position of the eye is in a parietal 
 foramen. The parietal cornea, pit, and spot are present. 
 
 2. Varanus bengalensis. Spencer ('86). 368 The pine'al organ 
 has a distal and proximal portion and there is no parietal nerve. 
 The parietal eye is present and contains a lumen. The retina 
 contains rod cells and several layers of smaller cells. The lens 
 is convexo-concave. The parietal foramen is of large size. 
 There is a capsule, a parietal pit, and a parietal spot. 
 
 3. Varanus nebulosus. Leydig ('91). 238 In this species the 
 pineal organ is as in other forms, but there is no end-sac. The 
 parietal eye is pyriform but there is no distinct retina. 
 
 4. Pseudopus pallasi. Owsiannikow ('88) ; 295 Hoffmann 
 ('90), 187 in Bronns "Klassen and Ordnungen." 
 
 In this form there is a well-developed lens, retina, and vitreous. 
 Studnicka 386 in 1895 described the conditions as follows: There 
 is a complete pineal organ with an end-vesicle, a stalk, and 
 proximal portion, the latter being the epiphysis. This is con- 
 nected with the brain-roof by a secondary stalk. The parietal 
 eye is semiglobuiar in shape. There is a lens and retina, the 
 
140 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 latter having rod cells, a layer of small cells and a layer of large, 
 probably ganglionic, cells. There is a parietal nerve and a con- 
 nective-tissue strand connecting the organ to the epiphysis. 
 The lens is bi-convex. An accessory organ is also present. 
 There is a capsule of connective-tissue and a broad parietal 
 foramen. A parietal cornea, pit, and spot also exist. 
 
 5. Varanus giganteus. Spencer ('86). 368 In this form there is 
 no mention of an epiphysis. The parietal nerve has a special 
 feature. From the end of the epiphysis to the parietal eye such 
 a nerve is seen to extend. Two or three strands of the nerve 
 are found which become confluent. The parietal eye is dorso- 
 ventrally flattened. There is a lens and retina present, the 
 latter contains rod cells and several other layers. In the cavity 
 there is a vitreus. The lens is thin and bi-convex. In the 
 center is a mass of round cells deeply pigmented indicative of a 
 rudimentary character of the organ. The parietal capsule con- 
 sists of connective tissue. There is a parietal foramen, pit, and 
 spot. 
 
 6. Varanus griseus. Edinger (00). 106 This species shows, in 
 a sagittal section through the brain, an unusually large epi- 
 physis thrown into many folds. It resembles the epiphysis of 
 Pseudopus. 
 
 TEJIDAE. 1. Ameiva corvina. Spencer ('86). 366 In this form 
 neither a parietal foramen nor a corneal pit is present. 
 
 2. Tejus teguixin. Klinckowstroem ('94). 209 An embryo of 
 this form seemed to show only a pineal organ well developed, 
 while above it was a rudimentary parietal eye. Studnicka 384 
 does not believe the parietal eye develops in this form. 
 
 LACERTIDAE. 1. Lacerta vivipara. Spencer ('86) ; 366 Owsian- 
 nikow ('88) ; 295 Strahl and Martin ('88) ; 383 Leydig ('91) ; 238 Stud- 
 nicka ('93). 384 In this species the pineal organ is globular and 
 pyriform; its extremity alone contains pigment. This is con- 
 nected with the parietal eye by a vascular connective-tissue 
 strand. The parietal nerve is independent of this strand. 
 The parietal eye is a flattened vesicle and there is a much-re- 
 duced lumen. The retina is deeply pigmented; its structure is 
 obscured by this vesicle. The lens is bi-convex. The capsule 
 
THE PINEAL BODY 141 
 
 is not well developed. The eye eventually makes its way into 
 the parietal foramen. The corneal pit is present. 
 
 2. Lacerta viridis. Spencer ( r 86); 366 Leydig ('91). 238 In this 
 form, extending from the parietal organ into the epiphysis is 
 a fibrous strand. The end of the epiphysis is deeply pigmented. 
 The parietal eye is flattened dorsoventrally. The retinolen- 
 ticular transition is gradual. There is much pigment in the 
 retina. The lens is bi-convex. The parietal foramen is present. 
 There is a corneal pit, cornea, and a parietal spot. 
 
 3. Lacerta ocellata. Spencer ('86) ; 366 Leydig ('91). 238 The 
 pineal organ is expended at its distal end with an end-sac proc- 
 ess. The wall is folded to form twelve accessory spaces in the 
 epiphysis. The end of the epiphysis is pigmented. There is a 
 parietal nerve and a well-developed parietal eye which is globu- 
 lar and slightly flattened. The retinolenticular transition is 
 gradual. The retina is pigmented and contains cylindrical and 
 ganglionic cells. The lens is bi-convex. The capsule is well 
 developed. The parietal foramen contains the eye. The 
 parietal cornea is present. There is also the parietal spot. 
 
 4. Lacerta agilis. Owsiannikow ('88) ; 295 Leydig ('91) ; 238 
 Studnicka ('93). 384 The pineal organ is present in the form of an 
 epiphysis, which is saccular and has a hollow stalk. The parietal 
 nerve, according to Leydig ('96), 239 is present. It takes origin in 
 the ganglion habenulae and extends to the parietal eye. This 
 eye is a flattened, saccular vesicle. The retina and lens are 
 sharply demarcated. The retina is less pigmented than in other 
 forms. It is connected with the brain by a parietal nerve. The 
 lens is bi-convex. There is a special parietal sheath made up of 
 connective tissue. The parietal foramen, corneal pit, and 
 parietal spot are present. Exceptionally, the foramen is closed 
 by bone. 
 
 5. Lacerta muralis. Leydig ('91) ; 238 Studnicka ('93) , 384 
 The epiphysis is present as is also the parietal eye. The retina 
 is deeply pigmented. The corneal pit and parietal spot are 
 also present. 
 
 SCINCIDAE. 1. Cyclodus gigas. Spencer '86). 366 The pineal 
 organ arches forward over the hemispheres to enter the region 
 
142 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 of the parietal foramen. The epiphysis is hollow. The stalk 
 opens into the ventricle. The proximal tubular portion is 
 present. The distal portion is within the foramen. The end- 
 vesicle of the pineal organ comes into this relation. Spencer 
 thought it was a rudimentary eye. The corneal pit, parietal 
 foramen, and parietal spot are present. 
 
 2. Chalcides tridactylus. Spencer ('86) ; 366 Leydig ('91). 238 
 The epiphysis is a globular vesicle. The end is prolonged into a 
 tapering process. The epithelium is much thickened. The 
 parietal eye is separate from the epiphysis. The retinolenticular 
 transition is gradual. The lens is bi-convex. There is a parietal 
 foramen, cornea, spot, and pit. 
 
 3. Hinulia. McKay ('88) ; 255 Sorensen ('94). 363 In this form 
 there is a well-developed parietal eye which is unattached to 
 the epiphysis. The lens is bi-convex. The retina contains 
 rod cells, round cells, a molecular layer, spindle cells, and pig- 
 ment cells. 
 
 4. Scincus officianalis. Prenant ('96). 313 There is a parietal 
 eye and a parietal foramen well developed in this form. 
 
 5. Gongylus ocellatus. Legge ('96). 228 In an embryonic 
 study of this form the epiphysis with a proximal portion and a 
 distal part was present. Only in the embryonic stages was the 
 parietal eye observed. It contains a brown pigment. There is 
 a lens which is bi-convex. The parietal nerve is not present. 
 The parietal cornea, foramen, and spot were not observed. 
 
 CHAMAELEONTIDAE. 1. Chamaeleon vulgaris. Spencer ('86) ; 366 
 Owsiannikow ('88); 2y5 Studnicka ('93). 384 The pineal organ in 
 the form of the epiphysis is a folliculated, hollow sac, which is 
 flexed forward, the walls being much flattened. It runs out into 
 a long, strand-like point. The parietal nerve is probably not 
 present in the adult. The connection between the pineal organ 
 and the eye is connective tissue and not nerve. As to the pari- 
 etal eye, authors differ; some say there is a good lens and retina, 
 others regard this as rudimentary in all respects. There is a 
 good capsule and a good parietal foramen. The parietal cornea, 
 pit, and spot are absent. 
 
 OFHIDIA. 1. Python ligris. Rabl-Ruckhard ('94). 323 In 
 this species there is an oval-shaped glandular structure, having 
 
THE PINEAL BODY 143 
 
 many reduplications in its walls. It is rich in blood vessels 
 and has a small cell content. Over it lies the chorioid plexus. 
 
 2. Eutaenia sirtalis. Sorensen ('94). 363 The epiphysis in this 
 species is globular in form and glandular in structure. It is 
 embedded in connective tissue. Herrick ('91) 176 agrees in these 
 observations. 
 
 3. Tropidonotus natrix. Studnicka ('93) ; 384 Leydig ('97). 24 
 In this form there is a paraphysis and epiphysis in older embryos 
 and in the adult. The epiphysis is definitely glandular in char- 
 acter. There is a thin stalk, the latter probably secondary 
 and not analogous to the stalk in lower forms. Ssobolew 364 in 
 1907, working on embryos of Tropidonotus natrix and Viper a 
 berus, found that the epiphysis develops earlier than the para- 
 physis. The parietal eye does not appear in either of the forms 
 studied, nor is there a parietal foramen. The cells of the epi- 
 physis are arranged in colonies as in the glands of internal secre- 
 tion. The organ seems to have nothing to do with light per- 
 ception and the same applies to heat perception. There is no 
 parietal nerve and the primitive canal in the organ is lost (fig. 69). 
 
 4. Tropidonotus rhombifer. Sorensen ('94) , 363 The epi- 
 physis is glandular in character. 
 
 5. Bascanium constrictor. Sorensen ('94). 363 In the embryo 
 of this species the epiphysis has a glandular form and is con- 
 nected with a stalk to the roof of the interbrain (fig. 70). 
 
 6. Coluber aesculapii. Studnicka ('93). 384 In this species 
 the epiphysis is globular in form and covered with connective 
 tissue. It contains a dark pigment and lies close to the brain. 
 
 7. Coronella austriaca. Leydig ('97). 24 There is no parietal 
 organ in this species in relation with the skull. In the embryo 
 the epiphysis is well developed. 
 
 8. Pelias berus. Hanitsch ('88); 169A Studnicka ('93). 384 In 
 this species Hanitsch believed that he discerned a parietal organ 
 with much pigment and a lens. Studnicka disagrees with this 
 and describes the epiphysis as a typically glandular structure. 
 
 9. Vipera ursinii. Leydig ('97). 24 In this species the struc- 
 ture is definitely glandular. 
 
 CHELONIA. 1. Chelone my das. Rabl-Ruckhard ('86). 322 In 
 this species the epiphysis is a massive, bilobed structure. 
 
144 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 2. Cistudo europaea. Bojanus ('19). 36 This author first 
 described the epiphysis in this form as a short, pediculated struc- 
 ure with a dilated extremity which was flexed forward. Faivre 115 
 in 1857 describes it as a conical body containing small particles of 
 calcium phosphate. Herrick 176 in 1891 defined it as a lobulated 
 sac attached to the roof of the brain. The distal portion is non- 
 vascular. Sorensen ('93), 361 reconstructed the pineal organ in 
 this form (fig. 71). 
 
 Fig. 69 The epiphyseal complex in a young Tropidonotus natrix, according 
 to Leydig, 1897. 
 
 3. Aspidonectes spinifer. Herrick ('9 1). 176 In this species 
 the epiphysis has the form of a tubular structure arching for- 
 ward. Its lumen opens into the ventricle through a short stalk. 
 
 4. Chelydra serpentina. Humphrey ('94). 19 The embryo 
 of this species has the same form as the saurians. In the early 
 stages it is a dilated sac connected with the third ventricle by a 
 short stalk. Later this stalk becomes hollow and in adults it 
 shows lobulation. 
 
THE PINEAL BODY 
 
 145 
 
 5. Amida mutica. Gage ('95). 136 The epiphysis in this 
 species is similar to other chelonians. 
 
 6. Chelone imbricata. Voeltzkow ('03). 41 The epiphysis in 
 this species is entirely separated from the brain. 
 
 Fig. 70 The pineal region of Boscanium constrictor, according to Sorensen, 
 1894. 
 
 P/., paraphysis; Ds., dorsal sac; Ch., commissura habenularis; Ep., proxi- 
 mal portion of pineal organ; Sch., pars intercalaris posterior; cp., posterior 
 commissure. 
 
 Crocodilia. Sorensen ('94). 363 As already stated, this author 
 did not find the epiphysis or any portion of the parietal organ 
 in the alligator. Voeltzkow 410 in 1903 in Crocodilus madagas* 
 cariensis found no epiphysis (fig. 72). 
 
 The conditions and relations of the epiphyseal complex 
 in Reptilia are so important as to necessitate the following 
 tabulation : 
 
 MEMOIR NO. 9 
 
1 
 
 s 
 l 
 
 ^ fl S -2 _ .2 
 
 Soi^^-ogG^ 
 
 iillliN 1 
 
 g p, 8 -! gj <; o 
 
 J --l 
 
 <; o o g b 
 
 *l 
 
 I G G G G G G 
 
 all III! 
 
 "5 <^ 
 
 2 -2 .s 
 
 G G G Bill 
 
 o o o o J3 
 
 Z PH PL, <J 
 
 O O O 
 
 O5 CO CO 
 G G G 
 
 m G "B "G 
 
 JJII 
 
 55 -! < < 
 
 Sp 
 
 | S 
 
 g ^ ^ 3 
 I 1 11 
 
 "^ .S 
 
 G 
 
 <! ^^ 
 
 8 
 III I 
 
 cc O O O O 
 
 146 
 
THE PINEAL BODY 
 
 147 
 
 Ds. 
 
 71 
 
 cp 
 
 Fig. 71 The pineal body of Cistudo europaea. according to Sorensen, 1896. 
 Fig. 72 The pineal region in the Alligator, according to Sorensen, 1896. 
 P/. ; paraphysis; Ds., dorsal sac; Ch., commissura habenularis; Cp., posterior 
 commissure; M., midbrain. 
 
148 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 The parietal or third eye does not make its appearance in 
 reptiles except in Sphenodon and Lacertilia vera. In these 
 latter forms it is by no means constant. Of forty-four species 
 examined, the parietal eye has been observed in 29 instances, 
 the retina in 28, the lens in 24, the parietal nerve in 25, the 
 cornea in 24, and the parietal foramen in 28. It was impossible 
 to detect these structures in the same number of species as 
 follows: Parietal eye absent in 9, retina absent in 11, lens absent 
 in 10, nerve absent in 12, cornea absent in 10, and parietal fora- 
 men absent in 10. The pineal organ, either complete in all its 
 three portions or as the proximal portion (epiphysis proper), 
 was present in all of the forty-four species. A complete pineal 
 organ was observed in thirty-one species while a highly devel- 
 oped proximal portion, possibly suggestive of glandular forma- 
 tion, was present in eight species. 
 
 In Ophidia and Chelonia there was a total absence of the 
 parietal eye and structures pertaining thereto in all of the fifteen 
 species examined. In nine species of ophidians the pineal 
 organ was represented in nine instances by a definitely glandular 
 proximal portion, the epiphysis proper or corpus pineale. This 
 gland seems to contribute its secretion to the ventricles, but 
 may also be of the blood- vascular type as well. In Chelonia 
 there is evidence that the pineal organ which appears as the 
 proximal portion of that structure may also be glandular in 
 nature. The absence of the parietal eye elements as well as the 
 pineal organ has already been mentioned in Crocodilia. 
 
 It is evident from this summary that only the proximal por- 
 tion of the pineal organ persists in the more modern reptiles, 
 while the parapineal element as well as the end- vesicle and stalk 
 of the pineal organ, have entirely disappeared. 
 
 7. Comparative Anatomy and Histology of the Epiphyseal Complex 
 
 in Birds 
 
 As in ophidians, the only element of the epiphyseal complex 
 which persists in birds is the proximal portion of the pineal 
 organ. This presents itself as the epiphysis or corpus pineale. 
 
THE PINEAL BODY 
 
 149 
 
 In form the avian epiphysis is conical or cylindrical, sometimes 
 being flattened by the approximation of the cerebellum and 
 cerebral hemispheres. Its size varies considerably in different 
 
 Fig. 73 The pineal region in Gallus domesticus, according to Studnicka, 1896. 
 Ds., dorsal sac; Ch., commissura habenularis; R., recessus pinealis; St., pineal 
 stalk; Ep., pineal body; Cp., commissura posterior. 
 
 species, but the following figures give a general idea of the 
 dimensions. 
 
 In Meleagris gallopavo 5 mm. long by 2.5 mm. thick 
 
 In Gallus domesticus 2.5 mm. long by 1.5 mm. thick 
 
 In Strix.. 6 mm. long 
 
150 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 It is situated close to the roof of the interbrain, its long axis 
 being as a rule, perpendicular to the latter. In no instance does 
 it approach or come in contact with the inner surface of the 
 skull. 
 
 The histology of the structure discloses several different 
 forms which the organ may assume. Studnicka ('05), 391 distin- 
 guishes three distinct types: 1) A long sac with thick walls con- 
 taining many follicles. Such an organ is found in Passer Gage 
 ('95). 136 2) A solid body with communicating or independent 
 acini which connect with the lumen of the pineal body by means 
 of a still potent canal. Between the follicles are many blood 
 vessels and much connective tissue. The stalk is solid as in 
 Meleagris gallopavo Mihalkovicz (77). 275 3) A solid organ in 
 which there are solid, blind acini instead of hollow follicles. 
 These acini make up solid lobules. 
 
 In brief, these three types may be termed, 1) saccular; 2) 
 follicular or acinal, and, 3) solid. There are a number of 
 transitional forms in addition to those already mentioned. 
 
 Funkquist 133 in 1912 describes two morphogenetic types in 
 birds. 
 
 1. The organ has a simple tubular character which, during 
 growth, shows a thickening of its walls and a general enlarge- 
 ment. In some cases the organ is solid except at its base where 
 it retains a cavity, the recessus pinealis. 
 
 2. In this type the organ has a tubular character, in many 
 instances retaining its connection with the original pineal evagi- 
 nation and in others being cut off from it. These bud-like 
 tubular processes resemble tubuli of the dorsal sac. The pineal 
 organ has its original anlage in an epithelial structure. Later, 
 development causes a transition into neuroglia tissue in much 
 the same way as the transition occurs in the central nervous 
 system. In some cases (canary and turkey) the acinus-for- 
 mation, giving rise to simple pineal tubules, persists, while in 
 other instances these acini are more or less obliterated. 
 
 Two types of cells may be identified, according to Funkquist, 
 namely, large epithelial cells with clear protoplasm and small 
 darkly staining cells. 
 
THE PINEAL BODY 
 
 151 
 
 Fig. 74. The pineal body in Coccothraustes vulgaris, according to Studnicka, 
 1896. 
 
152 
 
 FREDERICK TlLNEY AND LUTHER F. WARREN 
 
 Galeotti 140 in 1896 also recognized two types of cells, i.e., 
 radially arranged, cylindrical cells which bound the lumen of 
 
 Fig. 75 The pineal body in Meleagris gallopavo, according to Studnicka, 1896. 
 
 the organ and small cells between the larger ones. In the large, 
 cylindrical cells, Galeotti found hyaline masses which he con- 
 sidered a secretory product ultimately delivered to the lumen of 
 
THE PINEAL BODY 
 
 153 
 
 the acini. Studnicka 391 regarded these cells as ependymal in 
 type just as in the lower vertebrates, but found no sensory cells. 
 In addition to the ependymal elements there were neuroglia 
 cells, and Studnicka in Meleagris also observed some very large 
 cells with clear cytoplasm scattered among the other groups. 
 There may be ganglionic cells, as in Acipenser. No nerve fibers 
 were observed. The epiphysis contains many isolated cells and 
 a secretion derived apparently from the ependymal cells. No 
 pigment was observed. 
 
 
 Fig. 76 Section of the pineal body of Meleagris gallopavo, showing follicles, 
 .according to Studnicka, 1896. 
 
 The stalk of the epiphysis, which is of course in no sense 
 homologous Vith the stalk of the pineal organ, being a secondary 
 character of the epiphysis, is usually short and contains the 
 recessus pinealis. In some instances, however, it is solid. No 
 nerve fibers have been observed in it, so that the organ has no 
 neural connection with the brain. The epiphysis, including its 
 stalk or peduncle, is enclosed within a sheath of pia mater and 
 .arachnoid. 
 
154 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Klinckowstroem 206 in 1892 has shown in certain aquatic birds 
 during embryonic stages, a very early appearing, peculiarly 
 pigmented spot on the head. This he found in twelve out of 
 two hundred embryos of Sterna hirundo, Larus canus, Larus 
 marinus, Larus glaucus, and Anser brachyrhynchus. In adults 
 of these forms no such spot exists. There is little evidence to 
 indicate the tendency to the formation of a parietal foramen. 
 
 Dexter ('02) 90 observed in Gallus domesticus that the para- 
 physis is an appendix of the paraphyseal arch, developed from 
 the brain wall. He believes it to be glandular in character. 
 In the adult of this form it is composed of a modified ectodermic 
 tissue. In the younger stages its walls are thin and its cavity 
 is large, but in the adult chicken or hen the reverse is true. It is 
 oval in shape and lies nearly parallel with the longitudinal axis 
 of the cavity of the forebrain. It is a constant structure, and 
 Dexter has identified it time and again in the embryo, in the 
 chicken, and finally in the full-grown fowl. Its position is very 
 characteristic. The paraphysis is situated immediately dorsad 
 to the foramen of Munro and anterior to the prominent fold of 
 the chorioid plexus which must morphologically correspond to 
 the velum transversum. 
 
 Differences observed in the epiphyseal complex in the various 
 species of birds already investigated. . 
 
 1. Gallus domesticus. Stieda ('69) ; 376 Dexter ('02) ; 90 Galeotti 
 ('96). 14 It was observed in this form that the epiphysis is 
 follicular in structure and glandular in character. 
 
 2. Meleagris gallopavo. Mihalkovicz ('77) 275 observed that 
 the epiphysis is follicular in this form. 
 
 3. Sterna hirundo. Klinckowstroem ('92) 206 found remains of 
 the parietal spot in the embryo. 
 
 4. Anas domesticata. Klinckowstroem ('92). 206 In this form 
 the author observed that the epiphysis is follicular. 
 
 5. Apteryz. Parker ('92). 301 The epiphysis in this form is 
 usually anteflexed, although in some instances it is dorsiflexed. 
 
 6. Perdix cinerea. Studnicka (96). 386 The epiphysis in this 
 species is follicular. 
 
 7. Strix flammea. Studnicka ('96). 386 In this form the epi- 
 physis is partly solid and partly follicular. 
 
THE PINEAL BODY 155 
 
 8. Lanius excubitor. Studnicka ('96). 386 In this species the 
 epiphysis is saccular. 
 
 9. Turdus pilaris. Studnicka ('96). 386 The epiphysis is follic- 
 ular in this form. 
 
 10. Coccothraustes vulgaris. Studnicka ('96). 386 In this 
 species the epiphysis is hollow and saccular in its entire extent. 
 
 11. Passer domesiicus. Gage ('95). 136 The epiphysis is 
 hollow and saccular in this form. 
 
 In birds, as in ophidians, the evidence of the glandular nature 
 of the epiphysis is pronounced. Every form examined yields 
 many suggestive indications that the pineal body in birds is a 
 glandular organ. The element pertaining to the parietal eye 
 has not been observed in the avian forms examined and the 
 epiphysis is evidently the highly specialized proximal portion of 
 the pineal organ. The stalk and end- vesicle have disappeared. 
 The element referred to in birds as the stalk is something entirely 
 different from that portion of the lower forms which connects 
 the proximal portion and the end-vesicle. The avian stalk is a 
 secondary development consequent upon the marked enlarge- 
 ment and solidification of the proximal portion. During this 
 process the pineal body tends to move slightly away from the 
 roof, and in so doing produces an elongation in the originally 
 constricted area which connects the epiphysis with the roof of 
 the interbrain. This, in contradistinction to the stalk of the 
 end- vesicle, is the stalk or peduncle of the epiphysis. The pineal 
 recess contained within this peduncle is not entirely homologous 
 with the pineal recess of the lower forms, for in the latter in- 
 stances the recess extends into the proximal portion its entire 
 length, while in birds it is restricted to the peduncle. 
 
 8. Comparative anatomy and histology of the epiphyseal complex 
 
 in mammals 
 
 In mammals the only element of the epiphyseal complex 
 which persists is the proximal portion of the pineal organ. In 
 but a single instance thus far recorded is there evidence of the 
 parapineal element, i.e., Cutore's 74 observation of a small anterior 
 
156 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 protuberance in front of the epiphysis in the new-born Bos 
 taurus. As a rule, the proximal portion is solid in the greater 
 part of its extent and attached by a more or less constricted 
 portion to the roof of the interbrain. This part of the epiphysis, 
 sometimes referred to as the stalk, is not to be confused with the 
 stalk of the lower vertebrates which, together with the end- 
 vesicle, fails to develop in mammals. The mammalian stalk is 
 more properly designated the pineal peduncle. The solid por- 
 tion of the epiphysis is regarded by many as a glandular struc- 
 ture, and hence the term pineal gland. In mammals the follow- 
 ing parts may be defined: The epiphysis or pineal body which 
 consists of 1) the pineal gland and 2) the pineal peduncle. In 
 the latter there is a recess of greater or less extent, the pineal 
 recess. The peduncle consists in a large part of nerve fibers, 
 while the pineal gland comprises several different constituents. 
 In man the peduncle becomes so specialized in the nerve fibers 
 which enter it as to constitute, according to some authorities, 
 distinct peduncular bundles or epiphyseal peduncles. 
 
 The form of the pineal body in mammals varies considerably. 
 It is for the most part cone-shaped ; it may be long or relatively 
 short. In marsupials it is round or pyriform. In rodents it is, 
 according to Flesch, 121 more or less cylindrical, or, as Cutore 76 
 states, cylindricoconical. In the pig, d'Erchia 109 describes it as 
 spindle-shaped. In carnivores and primates the organ is gen- 
 erally conical or oval. According to Schwalbe ('81), 348 it is a 
 dorsoventrally flattened globule. In the primates the peduncle 
 is paired, with the exception of Troglodytes niger, in which, 
 according to M oiler ('90), 279 the epiphysis is kidney-shaped and 
 connected with the brain by means of a single unpaired stalk 
 4 mm. in length. The epiphysis in most mammals is dorsiflexed 
 so that its free extremity is directed toward the cerebellum. It 
 thus presents a ventral surface in relation with the midbrain, 
 a dorsal surface usually in relation with the corpus callosum 
 (although there are certain exceptions to this statement), a 
 base related to the roof of the interbrain, and an apex. The 
 dorsal surface is in contact with a reduplication of the dorsal 
 sac known as the lamina superior pediculorum and also with 
 
THE PINEAL BODY 
 
 157 
 
 the remnant of the pars intercalaris anterior forming the lamina 
 inferior. These two laminae form the walls of a cul-de-sac, the 
 suprapineal recess. The small space bounded by the pineal 
 peduncle is the pineal recess. 
 
 In regard to its relation to the corpus callosum, Cutore ('10) 76 
 states that there are three varieties of the pineal body in mam- 
 mals, i.e., 1) subcallosal, as in marsupials, some artiodactyla, 
 insectivora, carnivora, and primates; 2) retrocallosal, as in 
 most artiodactyla and perissodactyla ; 3) supracallosal, as in 
 rodents. Cutore ('10) 76 gives the following figures indicating 
 the relative weight of the pineal body to the brain and also 
 the pineal index: 
 
 ANIMAL 
 
 WEIGHT OP BRAIN 
 
 WEIGHT OF 
 EPIPHYSIS 
 
 PINEAL INDEX 
 
 Sheep 
 
 grams 
 
 480 00 
 
 grams 
 
 350 
 
 070 
 
 Pig... 
 
 140 00 
 
 040 
 
 020 
 
 Goat 
 
 119 80 
 
 075 
 
 060 
 
 Horse 
 
 512 00 
 
 440 
 
 080 
 
 Ass 
 
 420 00 
 
 520 
 
 100 
 
 Mule 
 
 430 00 
 
 860 
 
 0.200 
 
 Rabbit... 
 
 8 46 
 
 010 
 
 0.100 
 
 Rat 
 
 1 86 
 
 0.002 
 
 0.100 
 
 Dog.. 
 
 85 20 
 
 080 
 
 0.005 
 
 Man 
 
 1300 00 
 
 0.220 
 
 0.010 
 
 
 
 
 
 The following tables give the diameters of the pineal body in 
 man, according to several different observers, and also the 
 differences at different periods of development as reported by 
 Cutore: 76 
 
 Diameter of the pineal body in man in millimeters 
 
 
 HENLE 
 
 SCHWALBE 
 
 LORD 
 
 TESTUT 
 
 ROMITI 
 
 CHARPY 
 
 CUTORE 
 
 Longitudinal 
 
 8 
 
 12 
 
 5-9 
 
 7-8 
 
 12 
 
 10-12 
 
 9-10 
 
 Transverse 
 
 6 
 
 8 
 
 3-8 
 
 4-6 
 
 8 
 
 5-8 
 
 5-7 
 
 Anteroposterior 
 
 
 4 
 
 2-4 
 
 
 4 
 
 5 
 
 4-5 
 
158 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 AGE 
 
 SEX 
 
 WEIGHT OF 
 BODY 
 
 LENGTH OF 
 BODY 
 
 ANTEROPOSTER- 
 IOR DIAMETER 
 OF BRAIN 
 
 TRANSVERSE 
 DIAMETER 
 OF BRAIN 
 
 WEIGHT OF 
 BRAIN 
 
 WEIGHT OF 
 HYPOPHYSIS 
 
 WEIGHT OF 
 PINEAL BODY 
 
 Newborn 
 
 Female 
 
 grams 
 
 2,322 
 
 cm. 
 
 49 5 
 
 cm. 
 
 10 
 
 cm. 
 8 6 
 
 grams 
 
 340 
 
 grams 
 
 032 
 
 grams 
 007 
 
 8 days 
 
 Female 
 
 3,030 
 
 50.0 
 
 11.5 
 
 8.8 
 
 395 
 
 0.100 
 
 010 
 
 1 month 
 
 Female 
 
 2,207 
 
 52 
 
 11 5 
 
 9 4 
 
 470 
 
 100 
 
 040 
 
 3 months 
 6 months 
 
 Male 
 Male 
 
 3,700 
 5,700 
 
 63.0 
 67.0 
 
 13.8 
 14.9 
 
 11.4 
 10 8 
 
 762 
 793 
 
 0.110 
 115 
 
 0.035 
 053 
 
 10 months 
 
 Female 
 
 5,972 
 
 73 
 
 15 
 
 12 
 
 836 
 
 160 
 
 045 
 
 13 months 
 15 months 
 
 Female 
 Male 
 
 6,390 
 6,550 
 
 68.0 
 73 
 
 15.0 
 17 
 
 12.0 
 12 5 
 
 795 
 
 872 
 
 0.140 
 170 
 
 0.060 
 025 
 
 15 months 
 
 Male 
 
 4,248 
 
 73 
 
 14 4 
 
 11 
 
 507 
 
 120 
 
 080 
 
 18 months 
 
 Female 
 
 6,200 
 
 73.5 
 
 15.8 
 
 12.5 
 
 905 
 
 0.160 
 
 050 
 
 20 months 
 
 Female 
 
 6,722 
 
 74 
 
 15 3 
 
 11 3 
 
 710 
 
 180 
 
 060 
 
 3 years, 3 months 
 3 years, 6 months. . . . 
 4 years 
 
 Male 
 Male 
 Female 
 
 5,625 
 
 8,208 
 
 80.0 
 84.0 
 91 
 
 16.1 
 15.9 
 16 5 
 
 12.0 
 12.9 
 11 8 
 
 990 
 1,000 
 1,075 
 
 0.192 
 0.200 
 190 
 
 0.093 
 0.050 
 070 
 
 9 years 
 
 Male 
 
 
 115 
 
 17.7 
 
 14.3 
 
 1,100 
 
 0.250 
 
 100 
 
 11 years 
 
 Male 
 
 
 120 
 
 17 2 
 
 13 5 
 
 1,257 
 
 400 
 
 120 
 
 13 years 
 
 Female 
 
 
 130.0 
 
 16.7 
 
 13.1 
 
 1,219 
 
 0.340 
 
 0.170 
 
 18 years. . 
 
 Male 
 
 
 142 
 
 16 7 
 
 13 2 
 
 1,200 
 
 310 
 
 125 
 
 19 years 
 
 Female 
 
 
 150.0 
 
 17.5 
 
 13.1 
 
 1,193 
 
 0.320 
 
 0.060 
 
 22 years 
 
 Female 
 
 
 165 
 
 18.0 
 
 13.3 
 
 1,237 
 
 0.690 
 
 070 
 
 23 years 
 
 Male 
 
 
 162 
 
 16 9 
 
 12 5 
 
 1,162 
 
 780 
 
 120 
 
 24 years 
 
 Male 
 
 
 163.0 
 
 17.9 
 
 13.6 
 
 1,300 
 
 0.440 
 
 0.220 
 
 60 years. 
 
 Female 
 
 
 152 
 
 17 2 
 
 14 
 
 1,273 
 
 0.440 
 
 100 
 
 70 years 
 
 Female 
 
 
 147 
 
 16 9 
 
 13 
 
 1 000 
 
 650 
 
 140 
 
 70 years 
 
 Female 
 
 
 149.0 
 
 17.2 
 
 13.0 
 
 1,102 
 
 0.420 
 
 0.150 
 
 
 
 
 
 
 
 
 
 
 In the development of the pineal organ in all vertebrates, 
 only two of the germ layers play a part, i.e., the ectoderm and 
 the mesoderm. It is advantageous, therefore, in considering the 
 histological character of the pineal body, concerning which there 
 is much difference of opinion, to discuss the ectodermogenic 
 and mesodermogenic elements entering into that body. Of the 
 elements derived from the ectoderm the following have been 
 observed: 1) parenchymal cells, 2) ependymal cells, 3) neuroglial 
 cells, 4) ganglionic cells, and 5) nerve fibers. The following ele- 
 ments derived from the mesoderm have been described : 1) con- 
 nective tissue cells, 2) connective tissue trabeculae, 3) blood 
 
THE PINEAL BODY 159 
 
 vessels, 4) certain cells called muscle or myoid cells, 5) lympho- 
 cytes, and 6) lymphoid reticulum. 
 
 Hollard 188 in 1837 regarded the epiphysis as a glandular struc- 
 ture with nerve fibers in its peduncle only. Valentin 403 in 1843 
 believed that the pineal body possessed a parenchyma which 
 was something entirely different from the gray matter of the 
 brain. He observed certain 'nuclear formations ' which had a 
 striking resemblance to the tissue of the pituitary gland. Kolli- 
 ker 210 in 1850 described the epiphysis in mammals as consisting 
 of small, round cells, multipolar nerve cells and compact bundles 
 of nerve fibers. But it is to Faivre 114 in 1855 that we are 
 indebted for the first extensive study in the comparative his- 
 tology of the epiphysis. Faivre investigated microscopically 
 the pineal body of man, horse, guinea-pig, dog, ox, rabbit, and 
 pig. He recognized three elements in the human pineal body, 
 i.e., 1) a fibro vascular envelope, 2) a globular parenchyma, and 
 3) acervulus cerebri. Faivre's observation was in accord with 
 Valentin's, 403 that the pineal body differs essentially from the 
 brain. He concludes that the parenchyma is made up largely 
 of those globules which were nuclei of large elliptical cells in the 
 organ. He seems to have been the first to recognize that these 
 cells contained granules and also that the parenchymal cells 
 were smaller in the child than in the adult. Clarke 69 in 1860 
 found nerve fibers, nuclei and brain sand, but no nerve cells. 
 These elements were arranged in a reticular structure which 
 resembled the olfactory mucous membrane. Luys 253 in 1865 
 considered the organ as a structure composed of nerve cells 
 and fibers, in general, analogous to the mammillary bodies. 
 Leydig 232 in 1868 states that the pineal body in the mouse 
 resembles the pituitary gland in reptiles with certain small 
 differences. Frey ('67) 131 observed in adults multipolar gan- 
 glionic cells, rounded cells without prolongations and isolated 
 nerve tubes. Meynert (77)' 271 asserts that the parallelism 
 between the pituitary body and the epiphysis is a mistaken 
 idea. The pineal body should be considered a ganglionic deriva- 
 tive of the tegmentum. It contains two types of cells, one 
 having a diameter of 15 micromillimeters, the others 6 micro- 
 
160 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 millimeters in diameter. It differs from other ganglia only in 
 the fact that the cells are much closer together. Krause ('68) 219 
 described nerve fibers in the epiphyisis having a double contour. 
 Stieda ('69) 376 observed anastomosing processes of cytoplasm 
 with nuclei in a reticulum. Bizzozerp (7 1) 32 found two distinct 
 elements in the organ, namely, stroma consisting of prolongations 
 of the capsule and a definite parenchyma. In this latter were 
 two types of cells. In the larger of these the cytoplasm con- 
 tained granules. He noted that the pineal gland in the new- 
 born and in the infant contains the same elements as in the 
 adult. The only difference is in the fact that the smaller ele- 
 ments have a few branches while the larger cells have none. 
 The cells are arranged in alveoli. Meynert ('77) 271 concluded 
 that the epiphysis was a nerve ganglion. Hagemann (72) 164 
 found two types of epithelial cells, namely, round cells and 
 fusiform cells which are bipolar and multipolar nerve cells. 
 The pineal body, in his opinion, is a combination of epithelial 
 cells and nerve cells. Cruveilhier (77) 73 found in the epiphysis 
 pale, round cells, small nerve cells, large multipolar cells, and 
 calcareous concretions. Mihalkovicz (77) 275 concluded that the 
 pineal cells were not lymphatic corpuscles, but resembled the 
 cells in the lining of the cerebral ventricles. Schwalbe ('8 1) 348 
 considered the pineal cells to be modified epithelium with a 
 striking resemblance to lymphatic corpuscles. Cionini ('85- 
 '86) 66> 67 first demonstrated the presence of neuroglial elements,, 
 the nerve fibers observed belonging to the blood vessels. Dark- 
 schewitsch ('86) 79 refutes the idea that the pineal body is nothing 
 more than a 'simple gland.' By the Weigert method he found 
 the nerve fibers from the following sources: 1) internal capsule, 
 2) striae medullares, 3) Meynert's bundle, 4) optic tract, and 
 5) posterior commissure. Meynert 271 and Pawlowsky 305 have 
 already noted the connection between the posterior commissure 
 and the pineal body. Henle 172B in 1887 considered the pineal 
 body as a lymphatic ganglion. Its parenchyma consisted of 
 two types of cells, i.e., round cells resembling lymph corpuscles 
 and angular cells with many points. 
 
THE PINEAL BODY 
 
 161 
 
 Ellenberger ('87) no maintains that the pineal body in the 
 horse is very similar to a lymphatic gland. It is highly vascular; 
 in it are but a few nerve fibers and these are difficult to trace to 
 their origin. Flesch ('88) 123 studied the pineal body in the 
 horse, pig, dog, bat, and man. He was able to find brain sand 
 in man only. He does not believe that the organ is rudimentary, 
 but regards it as an epithelial structure. There are some nerve 
 
 Fig. 77 Follicles and parenchyma of pineal body in man, showing concretion 
 of brain sand, according to Henle, 1879. 
 
 fibers in it. Its relation to the size of the brain is not definite. 
 It has, in Fleseh's opinion, a physiological action in mammals, 
 is very vascular, while its specific cells contain pigment granules. 
 It seems to be a secretory organ and may contain a heat-regulat- 
 ing centre. 
 
 Edinger ( 7 97) 104 found the pineal body in the higher mammals 
 to be formed of neuroglia cells. True nerve elements are 
 absent. Chauveau ('85) 64 observed groups of polyhedral cells 
 
 MEMOIR NO. 9 
 
162 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 separated by connective-tissue trabeculae. He also mentions 
 calcareous deposits in domestic animals. Mingazzini ('89) 276 
 believes the pineal elements resemble lymphatic corpuscles. 
 Soury ('99) 365 found a substance like adenoid tissue filling the 
 spaces of a fine network. Weigert ('95) 419 describes the pineal 
 body, especially its ventral portion, as composed of a thick 
 layer of neuroglia fibers of such a specific nature that the like of 
 it is not found elsewhere in the central nervous system. The 
 cells are very numerous and traversed by many fibers. Cajal 
 ('95) 53 found sympathetic fibers entering the pineal body with 
 the vessels. These fibers form a rich interstitial plexus. The 
 fibers surround but do not penetrate the cytoplasm of the 
 glandular cells. Galeotti ('96-'97) 14 makes the claim that 
 the pineal body is a secretory organ and believes there is evi- 
 dence of this in many vertebrates besides mammals. The pineal 
 cells elaborate a pigment in addition to their secretory product. 
 He recognized nerve cells which are in relation with the superior 
 and posterior commissures, ependymal cells constituting the 
 middle portion of the body, in relation with the pineal recess, 
 and epithelial cells which constitute the epiphyseal tube in some 
 animals and the epiphysis in mammals. Lord ('99) 249 described 
 the parenchyma of the human pineal body as formed of small 
 stellate cells resembling those of adenoid tissue together with 
 other paler cells of variable size. Nicolas ('00) 283B found striated 
 muscle cells in the distal portion of the pineal body in the ox and 
 calf. Dimitrova ('01), 92 a pupil of Nicolas', studied the pineal 
 body in mammals, young and old, including man, ox, calf, sheep, 
 horse, dog, and cat. She maintains that Nicolas' observations 
 were confirmed by her studies and that striped muscle cells do 
 occur in the pineal body of the ox and calf. In her opinion, 
 the essential constituent of the epiphysis in mammals is neuroglia 
 and she concludes that in addition to the essential neuroglial 
 nature of the pineal body there exists in the ox, calf, sheep, and 
 dog certain cavities which resemble thyroid vesicles or the 
 anterior pituitary lobe. In young cats some cells which are 
 independent of the neuroglia seem to resemble the elements 
 described by Cajal 54 and Retzius 331A as sympathetic' and may be 
 
THE PINEAL BODY 
 
 163 
 
 Fig. 78 A striated muscle fiber from the pineal body of Bos taurus, according 
 to Dimitrova, 1901. 
 
164 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 neuroglia cells in process of development. Favaro ('04) 118 
 gives the following conclusions of his studies by means of the 
 Weigert method upon many mammals, including artiodactyla, 
 peris sodacty la, rodent ia, insectivora, carnivora, and primates. 
 Fibers found in relation to the pineal body are : 
 1. Prepineal fibers: 
 
 a) Transverse commissural 
 
 6) Oblique commissural 
 
 Fig. 79 Cells and fibers in the pineal body of Bos taurus (Weigert's method), 
 according to Dimitrova, 1901. 
 
 2. Fibrae seu fasciculus prepinealis. 
 
 3. Pineal fibers: 
 
 a) Superior transverse commissural fibers 
 6) Superior oblique commissural fibers 
 
 c) Posterior transverse commissural fibers 
 
 d) Diagonal commissural fibers 
 
 e) Superior and posterior fibrae propriae 
 
 Anglade and Ducos ('08-09) 5 found neuroglia constantly 
 present in the human pineal body but also alveoli-formed cells 
 
THE PINEAL BODY 165 
 
 of a different character. Sarteschi ('10) 345 found that, as com- 
 pared with the adult animals, the epiphysis in the young rabbit 
 and guinea-pig was distinctly more glandular and in this regard 
 similar to the organ in birds. In the course of growth certain 
 regressive changes occur. Neuroglia and glandular cells were 
 present in all of the forms which Sarteschi studied. Constantini 
 ('10) 71 studied the pineal body of the ox, horse, and man. He 
 describes two types of epithelial cells, i.e., 1) acidophiles and 
 2) basophiles. He concludes that the pineal body in mammals is 
 an organ of internal secretion. Cutore ('10), 76 on the basis of a 
 study of many different mammals, concludes that there are the 
 following histological elements in the pineal body: 1) Epithelial 
 cells containing granules and delimiting the cavities of tubules 
 or acini. 2) Lymphatic elements very numerous in larger 
 mammals and massed about the epipthelial cells. 3) Connec- 
 tive tissue forming trabeculae producing an apparent trabecula- 
 tion of the parenchyma. This connective tissue contains elastic 
 fibers, blood vessels, lymph spaces, and pigment cells probably 
 belonging to the category of mast cells. Some of the latter 
 cells give evidence of a process of fragmentation. 4) Cal- 
 careous concretions of calcium carbonate and phosphate. These 
 latter are sometimes found as inclusions in the cytoplasm or in 
 the meshes of the connective tissue. Cutore believes it to be an 
 organ of such complex structure, constituted of neuroglia, 
 epithelium, lymphatic and connective tissues, so arranged as to 
 form acini and so highly vascular, that it cannot be considered 
 to be in a state of regression as is claimed by Moller, 278 Charpy, 62 
 Dejerine, 85 and others. Indeed, the highly specialized and char- 
 acteristic structure of the pineal body is sufficient justification 
 to attribute to it an internal secretory function. Galasescu 
 and Urechia ( 7 10) 137 found in the vicinity of some of the blood 
 vessels round and oval cells with deeply staining nuclei situated 
 centrally in a cytoplasm which stains with acid stains, e.g., 
 eosin and fuchsin. The cytoplasm is granular and well demar- 
 cated. These acidophiles resemble those seen in the para- 
 thyroids. The authors propose to term these cells the 'para- 
 vascular acidophiles/ They believe these elements play a defi- 
 nite part in the internal secretion of the pineal body. 
 
166 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 A 
 
 c ^ 
 
 B 
 
 Fig. 80 Neuroglia cells in the human pineal body (Golgi's method), 
 cording to Cionini, 1889; B, according to Dimitrova, 1901. 
 
 A, ac- 
 
THE PINEAL BODY 
 
 167 
 
 Krabbe ( 7 11) 217 studied one hundred human pineal bodies, 
 both male and female, from birth to seven years of age and from 
 fourteen years to ninety-two years. There was a gap in his 
 subjects between the ages of seven and fourteen years. He 
 found two types of cells in the epiphysis: 1) special pineal cells 
 and 2) neuroglia cells. He thinks the granules in the cells leave 
 the protoplasm, traverse the intercellular space to enter the 
 blood, lymph, or cerebrospinal fluid, Krabbe does not agree 
 with Dimitrova 92 that the fundamental element of the pineal 
 
 Fig. 81 Cells with granular protoplasm in the pineal body of Bos taurus (Wei- 
 gert's method), according to Dimitrova, 1901. 
 
 body is neuroglia, for he considers her criteria in distinguishing 
 neuroglia insufficient. He himself never observed muscle fibers 
 in any of the forms which he has studied. Krabbe concludes 
 that the epiphysis in man shows certain signs of involution, 
 as, for example, concretions, hyperplasia of connective tissue, 
 neuroglial plaques with cysts, and the presence of cells in a state 
 of disintegration. The involution begins at seven years of 
 age, but even in the adult the pineal body shows signs of active 
 function. The secretory process is manifest in the following 
 
168 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 manner: 1) basophilic granules in the nuclei; 2) the latter evac- 
 uated into cytoplasm. This process goes on during the entire 
 life of the individual even into old age. 
 
 Biondi ('12) 49 calls attention to the finding of Constantini 71 
 and Galeotti 140 of acidophiles in the pineal body. Biondi made 
 a special study for mitochondria by the method of Regand. 
 He was able to demonstrate small granules which he thinks 
 must be regarded as mitochondria. This he cites as evidence 
 of the secretory nature of the epiphysis. He calls attention to 
 the fact, however, that Nageotte 281 and Mawas 263 have both 
 stated that neuroglia cells also contain mitochondria. 
 
 Jordan, ('II) 197 following the histogenesis of the pineal body 
 of the sheep, studied six stages from 5 cm. to 21 cm., also of the 
 eight months' lamb, yearling, and old sheep. He found no 
 muscle fibers. Between birth and the first year the pineal body 
 increases fivefold in size. In the fetus there are blind alveoli 
 and the organ is definitely lobulated by ingrowths from the pia. 
 Parenchymal cells form these alveoli. Vascular follicles are 
 abundant. The parenchyma consists of a more or less dif- 
 ferentiated ependyma. After the first year there are signs of 
 local degeneration manifesting themselves as an increase in con- 
 nective tissue, neuroglia, brain sand, clumps of pigment granules, 
 and a decrease of parenchymal cells. The entire pineal body 
 decreases in size after the first year. He concludes that there 
 is no cytologic evidence in favor of the secretory function of the 
 sheep's pineal body. He points out, however, that the general 
 structure of the epiphysis, including its lobulation, its connec- 
 tive tissue framework, its parenchymal follicles, blind alveoli, 
 perivascular lymph spaces, great vascularity, and presence of 
 cytoplasmic granules, is indicative of a glandular function of 
 internal secretion. He interprets the cysts which appear in the 
 pineal body and the melanic cytoplasmic granules as probably 
 having an ancestral significance. In Jordan's opinion, if the 
 pineal body subserves any important function at all, this is 
 true only of the first eight months of postnatal life. 
 
 Jordan 198 in the same year, studying the pineal body in the 
 opossum, states that the organ in this species has two forms: 
 
THE PINEAL BODY 
 
 169 
 
 Fig. 82 Transverse section of the pineal bod}' in the rat, according to Ramon 
 y CajaL 1904 
 
 a-6, sympathetic nerve fibers; c., interstitial nerve plexus; Bl., blood vessel; 
 Hm , hemisphere. 
 
170 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 
 Fig, 83 Histological characters of the pineal body in the sheep, according to 
 Jordan, 1911. 
 
THE PINEAL BODY 171 
 
 1) long and tubular, as in birds and reptiles; 2) short and 
 cup-shaped, resembling particularly that of carnivora. The 
 epiphysis is composed of a syncytial network, in the meshes of 
 which are scattered more or less highly differentiated or modified 
 ependymal cells and delicate bundles of nerve fibers. In the 
 opossum it appears to be in a state of instability. Its long, 
 tubular form connects it phylogenetically with the birds and 
 reptiles, while its short, cup-shaped form affiliates it with the 
 carnivora. Regarding the function of the pineal body in the 
 opossum, Jordan believes that his observations show it to be 
 unimportant in the body metabolism of mammals. This does 
 not necessarily mean that there is no specific secretion from 
 the organ, but rather that it has no direct or indirect influence 
 upon vegetative functions. 
 
 Nerve fibers in the mammalian epiphysis have been observed 
 by Kolliker 210 in 1850, who appears to be the first to demonstrate 
 these elements. Krause 219 in 1868 recognized the fact that the 
 fibers have a double contour, and Darkschewitsch 79 in 1886 
 showed that they were myelinated nerve fibers. Connections 
 have been demonstrated to exist between the pineal body by 
 means of these fibers with the following parts: 1) internal capsule; 
 
 2) striae medullares; 3) Meynert's bundle; 4) optic tract by 
 Darkschewitsch, ('86) 79 and 5) posterior commissure by Meynert 
 (77), 271 Pawlowsky (74), 305 Cionini ('88), 68 Favaro, ('04) 118 
 and Cutore ('10) ; 76 6) commissura habenularis by Kolliker ('50) 21 
 Hagemann (72), 164 Favaro ('04) 118 and Cutore ('10), 76 7) sym- 
 pathetic system, Henle (79), 172 Cionini ('86), 67 and Cajal 
 ('04). 54 Ganglion or nerve cells in the epiphysis have been 
 described by Kolliker 210 in 1850 and Hagemann 164 in 1872. 
 Cajal 53 in 1895 also found ganglion cells in the pineal body and 
 described two types. Dimitrova 92 in 1901 was able to find 
 ganglionic cells in young cats only. 
 
 Pigment has been found in the epiphysis of mammals by 
 Flesch 123 ('88). Galeotti ('96) 14 observed pigment particles in 
 the cytoplasm and nuclei. Dimitrova ('01) 92 found a golden- 
 brown pigment in the parenchymal cells. Cutore ('10) 76 ob- 
 served pigment in the pineal cells. Brain sand has been described 
 
172 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 by many authors in a number of mammals. Haller (1768) 165 
 considered it pathological, but Soemmering's 360 classical study 
 upon the acervulus clearly demonstrated that these concretions 
 are normal in man. Malacarne (1795) 258 found brain sand in 
 the epiphysis of the goat. Wenzel (1812) 420 described it in man 
 as being of two varieties according to its color, i.e., yellow or 
 white. Hagemann (72) 164 considered it a normal constituent 
 of the adult pineal body in man. He also observed it in the ox. 
 Krause ('76) 218 found it in many adult mammals. Flesch 123 
 describes brain sand in the epiphysis of the horse, sheep, pig, 
 and dog. 
 
 A parietal foramen has never been observed in mammals, but 
 the white spot which frequently appears in the frontal region of 
 the horse's head has been suggested as a vestigial indication of 
 this aperture in the skull seen in many of the lower vertebrates. 
 
 Differences observed in the epiphyseal complex in the various 
 species of mammals already investigated. 
 
 MARSUPIALS. 1. Macropus giganteus. Lotheissen ('94). 25 In 
 this species some nerve fibers penetrate into the substance of 
 the pineal gland. These come from the fasciculus retroflexus 
 of Meynert. 271 They were not observed in other mammals. 
 
 2. Halmaturus dorsalis. Condorelli-Francaviglia ('95). 70 In 
 this form, because of the rudimentary corpus callosum, the pineal 
 body extends dorsad between the hemispheres. Its length is 
 2 mm. and its thickness 1.5 mm. 
 
 3. Didelphys virginiana. Jordan ('II). 198 In the opossum 
 the pineal body occurs in two forms, i.e., either as a long tubular 
 organ or as a short, cup-shaped structure. It is composed of 
 ependymal cells in a syncytial network. 
 
 ARTIODACTYLA. 1. Bos taurus. Faivre ('55) ; 114 Hagemann 
 (72) ; i64 Chauveau ('85) 64 Nicolas ('00); 283B Dimitrova ('01) ; 92 
 Favaro ('04) ; 117 Constantini ('10); 7lA Cutore ('09). 74 In this 
 species the pineal body is cylindrico conical. Its diameters are : 
 
 cm. 
 
 Longitudinal 1.5 
 
 Transverse 0.7 
 
 Anteroposterior 0.7 
 
THE PINEAL BODY 173 
 
 It consists of large parenchymal cells, neuroglia, and lym- 
 phatic elements. It is very vascular. Cutore could find no 
 muscle cells. Some observers have found brain sand in the 
 organ. 
 
 2. Sus scrofa domesticus. Faivre ('55), 114 Hagemann (72) ; 164 
 Flesch ('87) ; 121 Favaro ('04) ; 118 Cutore ('10). 76 In this form the 
 pineal body is long and pointed toward its distal extremity. 
 Its diameters are: 
 
 CWl. 
 
 Longitudinal 1.0 
 
 Transverse 0.5 
 
 Anteroposterior 0.4 
 
 Fibers connect it with the ganglion habenulae and the pos- 
 terior commissure. It contains no concretions and no pigment. 
 Histologically it resembles the pineal body of Bos taurus. 
 
 3. Capra hircus. Malacarne ('95) ; 258 Hagemann (72) ; 164 
 Staderini ('97) ; 372 Cutore ('10). 76 In this species the pineal 
 body is relatively short and conical. Its diameters are: 
 
 cm. 
 
 Longitudinal 0.70 
 
 Transverse 0. 55 
 
 Anteroposterior 0.45 
 
 Malacarne described brain sand in the organ. Cutore could 
 find neither concretions nor pigment. Fibers connect the base 
 of the epiphysis to the posterior commissure and habenular 
 region. 
 
 4. Camelus dromedarius. Parisini. 300 In this form the author 
 described concretions. 
 
 5. Ovis aries. Flesch ("87) ; 127 Dimitrova ('01) ; 92 Favaro 
 ('04) ; 118 Jordan ('II). 199 In the adult of this species Jordan 
 describes signs of degeneration, including hyperplasia, brain 
 sand, clumps of pigment granules, and a decrease of parenchymal 
 cells. 
 
 PERISSODACTYLA. 1. Equus caballus. Faivre ('55) ; 114 Hage- 
 mann (72) ; 164 Ellenberger ('87) ; 110 Flesch ('88) ; 123 Favaro ('04) ; 118 
 Cutore ('10). 76 In this species the pineal body is conical. Its 
 diameters are: 
 
174 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 cm. 
 
 Longitudinal 0.8 
 
 Transverse 0.6 
 
 Anteroposterior 0.5 
 
 Nerve fibers are found in the base of the epiphysis. Histo- 
 logically, the pineal body consists principally of a delicate con- 
 nective-tissue framework, in the meshes of which are found 
 lymphatic elements. Many pigment cells are also found having 
 a brownish color and occupying usually a perivascular position. 
 Neuroglia and ependymal cells are also present. 
 
 2. Equus asinus. Cutore ('10). 76 In this species the pineal 
 body is larger than in the horse and its form is oval. Its diam- 
 eters are: 
 
 cm. 
 
 Longitudinal 1.5 
 
 Transverse 0.6 
 
 Anteroposterior 0.6 
 
 Its histology is much the same as that of the horse. Peri- 
 vascular pigmented cells are present in large numbers. 
 
 3. Equus mulus. Cutore ('10). 76 The pineal body in this 
 species is relatively large. Its diameters are: 
 
 cm. 
 
 Longitudinal 1.5 
 
 Transverse 0.6 
 
 Anteroposterior 0.6 
 
 It is conical in form. Histologically, it consists of paren- 
 chymal cells containing pigment granules. In addition, there 
 are ependymal cells, neuroglia, and lymphatic elements. 
 
 4. Elephas indicus. Parisini. 300 In this animal Parisini 
 reports the presence of concretions. 
 
 INSECTIVORA. 1. Erinaceus europaeus. Cutore ('10). 76 In 
 this species the epiphysis is triangular and is situated in the 
 inter collicular sulcus. It presents a well developed pineal recess. 
 Histologically, its elements resemble those of other mammals, 
 the cells being arranged in acini, not unlike the cellular forma- 
 tions in the hypophysis. 
 
 RODENTIA. 1. Talpa. Ganser ('82). 142 In this form the 
 pineal body was considered an unpaired ganglion habenulae. 
 It receives fibers from the thalami and the posterior commissure. 
 
THE PINEAL BODY 175 
 
 2. Lepus cuniculus. Tiedemann ('23) ; 395 Marshall ('61) ; 261 
 Krause ('68) ; 219 Bizzozero ('68) ; 30 Hagemann (72) ; 164 Mihalko- 
 vicz (77) ; 275 Edinger ('97) ; 104 Staderini ('97) ; 372 Neumayer 
 ('99) .282 Favaro (>Q4) ; 118 Cutore ('10) ; 76 Sarteschi ('10). 345 
 
 The pineal body in this species is long and cylindrical and of 
 such a shape as to justify the ancient term, penis cerebri. Its 
 diameters are: 
 
 cm. 
 
 Longitudinal ...................................................... 1.0 
 
 Transverse ........................................................ 0.3 
 
 Anteroposterior .................... ............................... 0.2 
 
 Its histological appearance resembles that of adenoid tissue. 
 There are no pigment cells and no concretions. 
 
 3. Cavia cobaya. Faivre ('55) ; 114 Hagemann (72) ; 164 d'Erchia 
 ('96) ; 109 Staderini ('97) ; 372 Favaro ('04) ; 118 Cutore ('10) ; 76 Sar- 
 teschi ('10). 345 In this species the pineal body is similar in form 
 to that of the rabbit. Its diameters are: 
 
 cm. 
 Longitudinal ................................................. ..... 0.8 
 
 Transverse ........................................................ 0.4 
 
 Anteroposterior ................................................... 0.3 
 
 Histologically, the organ resembles that of the rabbit. 
 4 Mus decumanus. Staderini '97 ; 372 Cutore ('10). 7G The 
 pineal body in this species is elongated. Its diameters are: 
 
 cm. 
 
 Longitudinal ...................................................... 0.5 
 
 Transverse ......................................................... 0.3 
 
 Histologically, it presents a rich vascularization and paren- 
 chymal cells similar to those of other rodents. Pigment and 
 calcareous concretions are absent. Neuroglia, nerve fibers, 
 elastic fibers, and lymphatic elements are also observed. 
 
 5. Dasyprocta agouti. Sperino and Balli ('09). 37 In this 
 species the form of the pineal body is cylindricoconical. Its 
 appearance is brownish, its apex is retroflexed so that the struc- 
 ture rests in the intercollicular sulcus. Its diameters are : 
 
 Longitudinal 
 Transverse.., 
 
176 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 CARNIVORA. 1. Phoca vitulina and Rosmarus obesus. Tur- 
 ner ('88) . 40 In the walrus and seal the pineal body has a greater 
 relative magnitude than in other mammals. 
 
 2. Canis familiaris. Tiedemann ('23) ; 395 Faivre ('55) ; 114 
 Flesch ('88) ; 123 Dimitrova ('01) ; 92 Favaro ('04) ; 118 Cutore; ('10). 76 
 In this species the pineal body is conical in form. It is relatively 
 small. Its diameters are: 
 
 cm. 
 
 Longitudinal 0.4 
 
 Transverse : 0.3 
 
 Anteroposterior 0.1 
 
 Histologically, it consists of neuroglia, nerve fibers, and 
 parenchymal cells which are polyhedral in form and arranged 
 in acini. Some cells contain pigment granules. In addition to 
 these elements there are large cylindrical ependymal cells. 
 There are no concretions present. 
 
 3. Felis domestica. Tilney ('15). 396 The pineal body in 
 the cat is even smaller than in the dog and it is ovoid in form. 
 Its diameters are: 
 
 COT. 
 
 Longitudinal . 20 
 
 Transverse 0. 15 
 
 Anteroposterior 0. 10 
 
 Histologically, it resembles the epiphysis of the dog. 
 
 4. Felis leo. Parisini. 300 This author described concretions 
 in the pineal body of the lion. 
 
 PRIMATES. 1. Troglodytes niger. Moller ('90) ; 278 Marshall 
 ('61) ; 261 Dendy and Nicolls ('II). 88 In this species the pineal 
 gland lies in a groove between the superior colliculi and has an 
 unpaired peduncle. There is a deep pineal recess and a well 
 developed suprapineal recess. No concretions were described 
 in this species. 
 
 2. Macacus sinicus. Cutore ('12). 76 In this species the di- 
 mensions of the pineal body are: 
 
 cm. 
 
 Longitudinal 0.5 
 
 Transverse 0.2 
 
 Anteroposterior 0.2 
 
THE PINEAL BODY 177 
 
 The pineal body is cylindricoconical in form in Macacus sinicus 
 and presents a great number of nerve fibers. 
 
 3. Cercopithecus griseus viridis. Cutore ('10). 76 In this 
 species the dimensions of the pineal body are: 
 
 cm. 
 
 Longitudinal 0.3 
 
 Transverse 0.2 
 
 Anteroposterior 0.2 
 
 The pineal body in this form is conical in shape. The struc- 
 ture of the organ is evidently glandular. 
 
 4. Homo sapiens. A large number of observers have given 
 their attention to the pineal body in man and many diverse 
 opinions have been expressed concerning it. Cutore's 76 sum- 
 mary giving the histology and dimensions of the pineal body in 
 man is the most recent and complete review. The figures have 
 already been cited (p. 157). Cutore concludes that the human 
 pineal body develops slowly, retaining even up to the time of 
 birth its primitive diverticular form. In the adult, however, 
 this organ has become relatively voluminous and the original 
 recess is much reduced to form the ventriculus or recessus 
 pinealis. The superior or habenular commissure is small. The 
 pineal fibers are limited in number and distributed to the inferior 
 third of the organ. In the disposition of the parenchyma there 
 is seen a distinct tendency for the cells to arrange themselves 
 in circular areas clearly delimiting small cavities in which there 
 appears an amorphous or crystalline substance. Elastic tissue 
 is scanty, but pigment cells are numerous and concretions of 
 varying sizes appear in large numbers. The vascularization is 
 rich especially around the aciniform groups of cells. Neuroglia 
 and cylindrical ependymal cells are also present. Connective- 
 tissue processes from the pia mater form an irregular partition 
 of the tissue into lobules. Siegneur 351 considers the pineal body 
 in man a gland, the cells of which are of two types, those which 
 are polyhedral with granules in the cytoplasm. These granules 
 are most numerous about the nucleus. Some of the cells have 
 vacuoles. The second type of cells are even larger and contain 
 large nuclei which stain deeply and occupy an excentric position in 
 
 MEMOIR NO. 
 
178 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 the protoplasm. In the new-born, lobation of the gland is much 
 more easily discerned than in the later periods of life. 
 
 The histology of the pineal body of the following mammals 
 has not heretofore been given, and as it seems to furnish some 
 details in the finer structure of the organ, the authors have 
 considered it advantageous to include these original observations 
 in this work. All of the material was obtained from the study 
 collections of the Department of Anatomy, Columbia University. 
 It includes specimens of Marcopus grayi, Camelus dromedarius, 
 Copra hylocrius, Zalophus calif ornianus, Lepus cuniculus, and 
 Simia satyrus. In addition to these species, the later stages of 
 development in the human fetus and in Felis domesiica were 
 studied. The staining methods used were the Van Giesen, 
 hsematoxylin-eosin, and Weigert's iron hsematoxylin. On ac- 
 count of the limited amount of tissue it was impossible to do 
 any silver impregnation so that no evidence was obtained con- 
 cerning the nature of the nerve fibers in the pineal body. 
 
 1. Macropus grayi. In this species the cellular constituents 
 of the pineal body present the most striking features of any 
 of the mammals studied. Four types of cells are noted: 
 
 First. Large cells with extensive cytoplasm and a large vesicu- 
 lar nucleus. The nuclei of these cells stain very deeply. 
 
 Second. Cells of a similar size with vesicular nuclei which 
 stain feebly. 
 
 Third. Smaller cells with a large nucleus and a very small 
 amount of cytoplasm. The nuclei are intensely basophilic. 
 
 Fourth. Small cells with feebly staining nuclei showing many 
 granules. 
 
 The cells of these four varieties arrange themselves in a more 
 or less distinctive manner. The large epithelial elements of 
 both types are disposed in such a way as to form well-defined 
 acini. Interspersed between these acinous groups are more or 
 less irregularly convoluted chains or cords of cells made up of 
 both varieties of the large type. The smaller cellular elements 
 are scattered among the cords and acini in an irregular manner. 
 Trabeculae of connective tissue serve to give the impression of 
 lobulation to the structure, although these lines of separation 
 
THE PINEAL BODY 179 
 
 are irregular. The pineal body of Macropus is highly vascular. 
 The larger vessels follow the lines of the connective-tissue sep- 
 tum. No concretions were observed in any part of the pineal 
 body. The impression given by the arrangement and char- 
 acter of the cells in the pineal body of this species is that of a 
 glandular structure resembling in a general way this organ in 
 reptiles and birds (fig. 84). 
 
 2. Capra hylocrius. In this animal four types of cells may be 
 distinguished, as in the kangaroo. Here, however, the large 
 elements with a deeply staining nuclei are more abdundant and 
 a smaller number of the small cells with pycnotic nuclei are 
 observed. The arrangement of the cells is typically aciniform, 
 although there are areas in which no such disposition of the 
 cells can be made out. These portions of the pineal body, 
 therefore, in which the acini do appear stand out conspicuously 
 in contrast to the areas of the tissue in which the cellular arrange- 
 ment is more diffuse. The size of the acini varies greatly from 
 about 10 micra to 60 or 70 micra in diameter. The connective 
 tissue observed in the pineal body of the ibex is prominent both 
 because of the extensive network which it forms and also on 
 account of the unusual thickness of its trabecular strands. The 
 body is highly vascular and supplied by a rich capillary network 
 (fig. 85). 
 
 3. Camelus dromedarius. In the camel, as in Capra hylocrius, 
 four types of cells may be differentiated, namely, the large cells 
 with deeply staining nuclei, large cells with faintly staining 
 nuclei in which nucleolus and accessory nucleoli are distin- 
 guishable, small cells with deeply staining, and small cells of 
 faintly staining nuclei. The cellular arrangement has the same 
 general appearance as in the ibex, although the tendency toward 
 the formation of acini is not as pronounced. In the main, the 
 arrangment is that of wide strands of cells bounded by irregu- 
 larly disposed trabeculae of connective tissue. The connective 
 tissue forms a prominent element in the pineal body of the camel 
 and in general resembles the connective tissue of the Persian 
 ibex. The pineal body in the camel is highly vascular. There 
 were no concretions observed in it (fig. 86). 
 
180 FREDERICK TILNEY AND LUTHER F. WARREN 
 
THE PINEAL BODY 
 
 181 
 
182 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
THE PINEAL BODY 183 
 
 4. Zalophus calif ornianus. In the sea-lion, although it is 
 difficult to discern the four types of cells already described with 
 clearness, as in the forms already noted, nevertheless, in certain 
 areas there appear many large cells with extensive nuclei which 
 stain deeply. Here and there scattered throughout the body 
 appear large cells of relatively the same size as those just men- 
 tioned, the nuclei of which, however, stain but faintly. Small 
 cells with deeply staining pycnotic nuclei are present in numbers 
 about equal to that of the first type while a small variety of 
 cell whose nucleus stains feebly is the least common variety 
 observed. The cells arrange themselves in cords or columns 
 which, upon transverse section, seem to be circular. These 
 cords apparently are much convoluted and not infrequently a 
 section of what appears to be the same cords is seen in transverse 
 as well as longitudinal outline. There is a rich connective tissue 
 network which appears to surround the cell cords. The pineal 
 body in Zalophus is highly vascular. No concretions were 
 observed (fig. 87). 
 
 5. Lepus cuniculus. In the rabbit the pineal body is long and 
 cylindrical in form. In it may be recognized the four types of 
 cells already described, the predominant type being the large 
 cell with abundant granular cytoplasm and a large deeply stain- 
 ing nucleus. Dispersed among these cells are small cells of both 
 types and the large cells with faintly staining nuclei. The 
 general arrangement of the cells in this body is that of columns 
 or cords whose long axes are transverse to the axis of the pineal 
 gland itself. The columns of cells are separated by delicate 
 trabeculae of connective tissue in the meshes of which capillary 
 vessels make their way. Each of the cell cords varies in thick- 
 ness in different parts. They are seldom more than six to 
 eight cells deep, but in some places their transverse diameter 
 seems to be the thickness of two cells. The gland is very vas- 
 cular and no concretions are seen (fig. 88). 
 
 6. Simia satyrus. In the orang, it is not difficult to recognize 
 the four types of cells already described in the other forms. 
 Perhaps the chief difference in the histology of the gland in 
 this animal is the great prominence which the large cells attain 
 
184 FREDERICK TILNEY AND LUTHER F. WARREN 
 
THE PINEAL BODY 
 
 185 
 
186 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 both because of their tendency to be collected into well-defined 
 groups, as well as the unusual dimensions of their cytoplasm. 
 Here, as in none of the other forms already described, does the 
 character of the pineal cell stand out. Not only is it much 
 larger, but it has the granular appearance so notable in the 
 human pineal cell. The large cells with the faintly staining 
 nuclei are found scattered among the cells just mentioned and 
 also scattered diffusely throughout the organ. The small cells 
 are less prominent, although both types may be recognized. 
 The cells are arranged according to an apparent design, although 
 the large pineal cells group themselves in irregular masses. 
 No tendency to cord formation is, however, observed. There 
 is a rich and delicate network of connective tissue, and many 
 capillaries surround the cell masses. No concretions were 
 observed (fig. 89). 
 
 7. Homo sapiens. In the adult human pineal body the types 
 of cells already described as present in the epiphysis of other 
 mammals may be observed here also. The large cells with 
 granular cytoplasm and large deeply staining nuclei are the 
 most prominent elements. They are arranged in regular masses 
 very similar to those observed in Simia saiyrus, although the 
 intervening areas are less extensive, so that in man the cell 
 masses seem to run into each other without sharp line of demar- 
 cation. A very dense network of connective-tissue trabeculae 
 forms the frame work of the organ, while the vascularity of the 
 structure is richer than that of any other form observed. Con- 
 cretions of varying sizes are present throughout the entire 
 gland (fig. 90). 
 
 The histogenesis of the pineal gland was studied in the cat 
 and human. The inception of differentiation in the cat presents 
 itself as a marked thickening in the walls of the more caudal of 
 the two evaginations. In the 70 mm. cat this thickening is so 
 pronounced that the recess in the anlage is reduced to a narrow 
 lumen. The cells multiply at the caudal extremity of the now 
 almost solid epiphysis. From the stage of 120 mm. to term a 
 process of diverticular formation occurs. This starts at the 
 base of the gland at its attachment to the roof -plate and grad- 
 
THE PINEAL BODY 
 
 187 
 
 ; 
 
188 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 *A.-?V *Jk /* r tf 1P5 
 
THE PINEAL BODY 189 
 
 ually extends to its distal extremity. Many of these diver- 
 ticula remain in connection with the third ventricle, but as they 
 elongate toward the tip of the pineal body many of the diver- 
 ticula lose this connection and finally appear as blind acini or 
 cell cords. In this way the original more or less indifferent cell 
 area of the primitive anlage is invaded by cells from the diver- 
 ticula above described. Simultaneous with the invasion of 
 these diverticula, blood vessels are seen to make their way into 
 the tissue between the acini and cell cords. This vascular 
 invasion seems to take place from the periphery going to the 
 center, but it is possible that independent blood spaces are 
 formed which, by concresence, subsequently form a vascular 
 network, the latter coming into relation with the blood vessels 
 surrounding the pineal body. These characters of the onto- 
 genesis of the pineal body in the cat are shown in figure 91. 
 
 The process just described in the histogenesis of the cat is 
 much better illustrated in the development of the human fetus. 
 In man, the process of diverticular invasion into the original 
 cellular mass of the primitive anlage is well shown in figure 92, 
 representing the condition in a human fetus of six months. Here 
 it will be noted that the invasion begins at the base of the epi- 
 physis and manifests itself in the thick strand of darkly staining 
 cells extending out and into a mass of undifferentiated tissue. 
 At term the invasion has extended completely through the epi- 
 physis and the deeply staining strands of cells are now arranged 
 in convoluted cords or take the form of apparent acini. In the 
 meshes between these cords capillaries appear to have made 
 their way in from the surface of the epiphysis and form a rich 
 network about the cell cords and apparent acini. This onto- 
 genetic differentiation in the two forms just described would 
 certainly seem to indicate a process which had as its object the 
 rich vascularization of discretely outlined epithelial areas. Such 
 a differentiation would seem to adapt itself best to the purposes 
 of internal secretion. 
 
 Marburg 259 shows in the development of the pineal gland in 
 man histological appearances very closely resembling those 
 illustrated in figures 91, 92, 93, and 94 of the authors (fig. 95). 
 
190 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 ,-> t-. 
 
 ^^HH ^ 
 
 i j^yr _/ 2 
 
 -.,.*.,*. - 
 
 EH 
 
 
 
THE PINEAL BODY 
 
 191 
 
 Fig. 92 Section of the pineal body in a six months human fetus showing the 
 diverticular invasion, according to Tilney and Warren, 1917. 
 
192 
 
 FBEDEBXCK TI LNEY AND 
 
 ^ 
 
 J 
 
THE PINEAL BODY 
 
 193 
 
 MEMOIR NO. 9 
 
194 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Marburg also gives an interesting description of the develop- 
 ment of the suprapineal recess in man which is illustrated in 
 figure 96. According to his description, the suprapineal recess 
 is formed by the dorsal reflection of the taenia which originally 
 was directed cephalad. The dorsal surface of the taenia secon- 
 darily becomes fused with the dorsal surface of the pineal gland 
 while -the ventral surface is turned dorsad. In this way the 
 suprapineal recess results from a deep evagination of the roof- 
 
 Fig. 95 Cross section of the pineal gland in a 26 mm. human embryo, according 
 to Marburg, 1909. 
 
 plate which comes to lie above the pineal body and extends in 
 most cases the entire length of that organ. The suprapineal 
 recess in its relation to the pineal gland in adult man is shown in 
 figure 97. 
 
 With reference to the pineal body Marburg maintains that in 
 spite of all the involution processes in the gland, it cannot be 
 denied that even up to the late periods of life in man there are 
 wholly intact glandular cells present in the organ which must 
 certainly be taken to indicate a still existing function. 
 
^ - 
 
 97 
 
 Fig. 96 Scheme showing the development of the supra-pineal recess, according 
 to Marburg, 1909. 
 
 Fig. 97 The pineal gland in man, according to Marburg, 1909. 
 
 Ch., commissura habenularis; Cp., commissura posterior; Pl.ch., chorioid 
 plexus; Rp., recessus pinealis; Rs, recessus suprapinealis; Sch., pars intercalaris; 
 Th., taenia habenulae; Z, pineal gland. 
 
196 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 7. DISCUSSION 
 
 1. Significance of the pineal region 
 
 It is now possible, with the facts presented as evidence, to 
 discuss the problem of the pineal body and, perhaps, to formu- 
 late some conclusions concerning it. 
 
 The question uppermost about the epiphysis to-day is whether 
 the structure is a mere vestige or whether it has, in mammals 
 and more especially in man, some definite function. Besides 
 this highly important consideration there is still another which, 
 in its way, has an even more far-reaching significance, namely, 
 the value of the pineal structures as one of the indices which may 
 point out the lines of evolution running through the vertebrate 
 phylum and those leading back to the invertebrate, ancestral 
 stock. 
 
 If the pineal body is a vestige, it is essential to ascertain to 
 what previously active structures it is related and for what 
 reasons it has become vestigial. In this sense the survey of its 
 phylogenetic relations cannot be too broad and should include 
 the entire environment of the organ. If, as is held by many, the 
 pineal organs have significance as a connecting link between 
 the vertebrates and invertebrates, then, on the basis of embry- 
 ology and comparative morphology, the' effort must be made to 
 homologize not one, but all of the parts associated with or 
 adjacent to the pineal body. In such a light every derivative 
 of the roof-plate of the primitive forebrain becomes funda- 
 mentally important, and no discussion of the pineal body could 
 be complete which did not recognize the character of the pineal 
 region as a whole. 
 
 The portion of the brain known as the pineal region was first 
 so designated by Minot 277 in 1901. It has also been termed the 
 parietal region. It extends from the dorsal extremity of the 
 lamina terminalis to the caudal limit of the posterior commissure 
 and comprises a,ll of the structures which develop from the roof- 
 plate of the primitive forebrain. It presents, according to 
 Minot, 277 a series of three arches or vaults, arranged one in 
 front of the other. The most cephalic of the three arches is 
 
THE PINEAL BODY 197 
 
 the paraphyseal arch, which extends from the dorsal extremity 
 of the lamina terminalis to the most cephalic depression in the 
 roof, namely, the velum transversum. The portion of the roof 
 immediately caudad of the velum forms the middle or postvelar 
 arch, which in turn is separated from the third or caudalmost 
 arch by a slight depression containing the superior or habenular 
 commissure. This is the epiphyseal arch. In some species a 
 small intercalated portion of modified gray matter inserts itself 
 between the caudal limit of the postvelar arch and the superior 
 commissure. This is the pars intercalaris anterior. Caudally, 
 the epiphyseal arch extends toward the cephalic extremity of 
 the posterior commissure, but between the latter and the caudal 
 extremity of the arch there is interposed a small area of modified 
 gray matter, the pars intercalaris posterior. The caudalmost 
 element in the pineal region is the posterior commissure, and to 
 this, perhaps, should be added the subcommissural organ, recently 
 described by Dendy and Nicolls 88 and others. 
 
 These structures of the pineal region or their homologues exist 
 in all vertebrates either in the embryonic or adult condition. 
 The paraphyseal or pre velar arch is common to all vertebrates. 
 From its caudal portion, i.e., the region of the arch nearest the 
 velum transversum, there develops a specialized structure, the 
 paraphysis. This structure, either in anlage or as an adult 
 organ, appears in all vertebrates. 
 
 In cyclostomes (Kupffer 224 in Ammoccetes, Burckhardt 47 in 
 Petromyzon) the paraphysis is a small sac-like diverticulum, if 
 not itself highly vascular yet in close relation with the vascular 
 mesenchyme immediately above it. In selachians (Minot 277 
 and Locy 243 in Acanthias) the structure is a small outgrowth 
 from the paraphyseal arch. In ganoids (Kupffer 223 in Acipenser, 
 Hill, 180 Eycleshymer and Davis 113 in Amid) the paraphysis is a 
 large diverticulated and vascular organ. In many teleosts 
 (Burckhardt, 47 Studnicka, 391 and Terry) 392 the paraphysis appears 
 to be rudimentary. In dipnoians (Burckhardt 44 in Protopterus) 
 the organ is a wide outgrowth with many small diverticula and 
 rich in blood vessels. The paraphysis in amphibians attains its 
 greatest conspicuity as an organ. It is highly differentiated in 
 
198 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 the adult (Warren 416 in Necturus, Osborn 289 in Siredon, Siren 
 and Proteus.) It is an elaborately folded, glandular structure 
 (Burckhardt 43 in Triton and Ichthyophis) , a solid vascular 
 mass (Sorensen 361 in Menopoma), or a tubular and digitated 
 structure (Eycleshymer 112 in Amblystoma). In Rana, accord- 
 ing to Minot, 277 the paraphysis is characterized by a glandular 
 epithelium, a tubular arrangement of its cells, and an appar- 
 ently sinusoidal circulation, In Lacertilia (Warren 415 in Lacerta 
 muralis, L. agilis and L. viridis) it is large and glandular in 
 character, forming a conspicuous element of the pineal region. 
 In many instances it is so extensive as to reach caudad as far 
 as the midbrain, or even the cerebellum. In ophidians, chelo- 
 nians and crocodilians, the paraphysis is small and rudimentary. 
 In birds it was first demonstrated in the chick by Selenka 352 and 
 later described by Minot 277 in the chick and Burckhardt 46 in 
 the embryo crow. Dexter 90 found it constant in the chick and 
 common fowl. He believes it to be a gland in which there are 
 no sensory elements. 
 
 In mammals Selenka 352 gave the first description of the para- 
 physis in the opossum. Francotte 128 observed it in a 12 mm. 
 human embryo. Usually, however, although it has been recog- 
 nized in anlage, in mammals it disappears early and the para- 
 physeal arch bears no trace of it in the 'fetal period. 
 
 Thus it will be seen that the glandular nature of the para- 
 physis in the middle portion of the phyletic series, including 
 amphibia and lacertilia, is quite beyond dispute. Some of this 
 character it retains in the more modern reptiles and birds. On 
 the other hand, it is relatively inconspicuous as an organ among 
 the lowest vertebrates and disappears altogether is most mam- 
 mals. Manifestly, therefore, whatever tendency toward speciali- 
 zation the paraphysis presents is in the interest of glandular 
 formation. As a gland, it appears either to contribute its secre- 
 tion directly to the cerebrospinal fluid in the ventricles or in- 
 directly to the blood. In no instance is there evidence of a 
 tendency toward the development of sensory structure nor do 
 the histological elements entering into the paraphysis suggest 
 its direct participation in any neural mechanism. 
 
THE PINEAL BODY 199 
 
 From the remainder of the paraphyseal arch there develop 
 in many classes of vertebrates several chorioidal processes. In 
 cyclostomes, selachians, teleosts, and ganoids, two such plexuses, 
 more or less well developed, may be recognized, namely, the 
 lateral and inferior telencephalic chorioid plexuses. The inferior 
 chorioid plexus attains its most marked proportions in amphibia, 
 while in all of the higher vertebrates its prominence declines. 
 This is likewise true of the lateral chorioid plexus. Histologi- 
 cally and topographically, the significance of these plexuses is 
 not difficult to discern; their rich vascularization, their tendency 
 toward glomerular arrangement together with the relations and 
 modifications of the ependymal cells which enter into them 
 leave little room to doubt that they are glandular in nature. 
 Indeed, the present tendency is to refer to these structures as 
 chorioidal glands, thus deputing to them a definite, secretory 
 function in relation to the cerebrospinal fluid. Even the older 
 conceptions of the chorioid plexuses recognized this physio- 
 logical possibility in connection with the plexuses. 
 
 The morphological fact concerning the first and most cephalic 
 of the three arches in the pineal region discloses a predominant 
 tendency for its derivatives to give rise to glandular structures, 
 while, on the other hand, there is no evidence that it has ever 
 been engaged in definite neural mechanisms. 
 
 The structure which forms the boundary between the prevelar 
 or paraphyseal arch and the postvelar arch is the velum trans- 
 versum. Like the paraphyseal arch, it attains its greatest con- 
 spicuity in the lower vertebrates and in the higher forms becomes 
 less prominent. In mammals its appearance is most pronounced 
 in the embryonic period from which time it becomes progres- 
 sively reduced, being present in the adults of most orders as a 
 more or less well-marked rudiment. In most classes of verte- 
 brates it becomes associated with a dense mesenchymatous in- 
 vasion which results in a fairly rich vascularization. This com- 
 bination of ependymal cells and blood vessels often takes the form 
 of a plexus, and when such is the case the velum transversum 
 aligns itself with the structures derived from the paraphyseal 
 arch in the absence of any definitely neural elements and ths 
 tendency toward glandular formation. 
 
200 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 The middle or post velar arch (so called by Minot 277 ) in the 
 pineal region has also been designated the Zirbelpolster by 
 Burckhardt, 47 the postparaphysis by Sorensen, 361 the dorsal sac 
 by Goronowitsch, 153 and the roof of the parencephalon by 
 Kupffer. 226 This structure, with few exceptions, forms a prom- 
 inent element of the pineal region throughout the vertebrate 
 series. In cyclostomes it is present as a simple membranous 
 sac with scant vascularity of its own, although in close approxi- 
 mation with the highly vascular mesenchyme dorsal to it. In 
 selachians it is usually somewhat more extensive yet similar in 
 its structural details. In ganoids it becomes immensely ex- 
 panded as shown by Balfour, 11 Huxley, 191 Wiedersheim, 425 
 Goronowitsch, 153 Wilder, 428 and Kingsbury. 204 Herrick 178 describes 
 the dorsal sac as a pouch lined with a single row of ependymal 
 cells with long cilia which appear to be of the epithelial, secre- 
 tory type. It is highly vascular in these fish. In teleosts, on 
 the other hand, it is not always prominent, In Opsanus, Terry 392 
 found that the dorsal sac was small and perhaps disappeared 
 altogether. In some teleosts, as in ganoids, the postvelar arch 
 is not only highly vascular, but presents ridges, secondary folds, 
 and diverticula. In amphibia, reptiles, and birds, the postvelar 
 arch becomes definitely associated with the formation of the 
 chorioid plexuses, and it does, in fact, contribute the epipthelial 
 elements to the chorioid plexus of the diencephalon. With the 
 advent of the corpus callosum in mammals the dorsal sac or 
 postvelar arch becomes somewhat overshadowed, due to the 
 introduction of the transverse commissure which lies above and 
 tends to flatten it. It, however, loses none of its tendency to 
 participate in the plexus formation, which latter in mammals 
 -attains a greater development than in many of the lower forms. 
 
 This element of the pineal region, therefore, is to be associated 
 with the paraphyseal arch in its tendency toward specialization 
 From the lowest vertebrates upward through the phylum it 
 manifests no attempt toward the development of sensory or 
 other definitely neural elements, while the entire trend of its 
 evolution reveals a glandiferous potentiality. 
 
THE PINEAL BODY 201 
 
 The postvelar arch is separated from the caudalmost or epi- 
 physeal arch of the pineal region by a shallow invagination of 
 the diencephalic roof, which usually contains commissural 
 nerve fibers. This is known as the superior commissure or 
 commissura habenularis. In some forms, as in amphibia, it is 
 associated with a small, somewhat thickened area of the roof in 
 which the histological elements are largely neuroglia. This is 
 the pars intercalaris anterior. Although the structure, or its 
 homologue, occurs in such a limited number of animals, its 
 recognition as a distinct part seems advisable in the description 
 of this area of the brain. In cyclostomes, prosaurians, and 
 saurians, the superior or habenular commissure seems to be 
 connected with the parapineal or parietal nerve and, perhaps, 
 through this relation is brought into connection with the end- 
 vesicle of the parapineal organ. If such is the case, it may well 
 be that this commissure in cyclostomes, in prosaurians, and in 
 saurians is related to an organ of special sense. In this light 
 the superior commissure must be accounted as engaged in the 
 organization of a specialized neural mechanism, and thus be- 
 comes the first of the structures encountered in the pineal region 
 to show this tendency in differentiation. The significance of the 
 pars intercalaris anterior is not altogether clear, although it is 
 possible that it may represent a residue of an unutilized susten- 
 tacular area developed in the interest of the commissural forma- 
 tion. The presence in it of a few nerve fibers would seem to 
 substantiate this view. 
 
 The caudalmost or epiphyseal arch is by far the most complex 
 of the three arches in the pineal region. In order that its de- 
 scription may be comprehensive enough to include all verte- 
 brates, a number of different elements are to be recognized, 
 either as appearing in the embryo or giving rise to definite adult 
 structures whose composit may, for convenience, be termed the 
 epiphyseal complex. This complex, then, consists of two princi- 
 pal organs, namely, the pineal organ and the parapineal organ. 
 Each of these organs is in turn susceptible of subdivision into 
 certain portions as follows: 
 
202 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 1. Pineal organ. 2. Parapineal organ. 
 
 a) Proximal portion. a) Proximal portion. 
 
 6) Stalk. b) Stalk. 
 
 c) End-vesicle. c) End-vesicle. 
 
 Of all of these parts the proximal portion of the pineal organ 
 is phyletically the most constant, occurring in all classes of 
 vertebrates. The stalk and end- vesicle of the pineal organ 
 are much less constant, for they cease to appear in ophidians 
 and are absent in all the forms higher than the snakes. The 
 parapineal organ as a whole is limited to but a few classes of 
 vertebrates. It is prominent only in cyclostomes, in prosaurians 
 and saurians. It is rudimentary in ganoids and teleosts. It is 
 developmentally transitory or entirely absent in selachians, 
 amphibia, ophidians, chelonia, crocodilians, birds, and mammals. 
 
 Considered, for a moment, quite apart from the inferences 
 which may be drawn from the intrinsic structural characters of 
 the epiphyseal complex itself, there is one outstanding feature 
 of unquestionable importance, namely, the genetic association of 
 this complex with a series of organs which under no conditions 
 have manifested a tendency to become specialized in the interest 
 of definitive neural mechanisms, but which, wherever differ- 
 entiated, have given rise to glandular tissue. 
 
 The caudalmost element in the pineal region is the posterior 
 commissure. It is, perhaps, not definitely settled that this 
 assignment of the commissure to the interbrain is in all respects 
 justifiable. If, however, it is to be accounted as a structure of 
 the pineal region, the function of the commissure appears to be 
 related to a specialized portion of the pineal organ, namely, the 
 end- vesicle, with which latter the posterior commissure is said to 
 be in connection by means of nerve fibers. Admitting, for the 
 moment, the correctness of the morphological and physiological 
 interpretation given the subcommissural body by Dendy and 
 Nicolls, 88 the structure may tentatively be considered as a 
 part of the pineal region. Its function, apparently, is in some 
 way connected with the fiber of Reissner and the entire organ 
 thus associated with equilibration. Both of these elements, 
 
THE PINEAL BODY 203 
 
 constituting the caudalmost constituents of the pineal region, 
 are obviously specialized as neural mechanisms in the interest of 
 special sense receptors. The pars intercalaris posterior has, no 
 doubt, the same functional significance as the anterior inter- 
 calated area associated with the superior commissure. 
 
 From a review of the several structures associated with the 
 epiphyseal complex in the pineal region, it is clear that the 
 majority of them when differentiated at all give rise to glandular 
 organs, while those which participate in neural mechanisms are 
 not only in the minority, but constitute a relatively small portion 
 of this area in the brain. Thus the paraphysis and paraphyseal 
 arch as a whole, the velum transversum, and the post velar arch 
 are genetically glandiferous, while the superior commissure and 
 posterior commissure alone bear any apparent relation to neural 
 activity. 
 
 In view of these facts, it would seem that whatever the func- 
 tions of the epiphyseal complex may be, the morphogenetic 
 impulse imparted to it from a region of the brain so preponder- 
 atingly glandiferious in its constituents could not fail to have 
 a profound influence upon the evolutional adaptation of the 
 epiphysis. Yet, in spite of the illumination which this genetic 
 association of the epiphyseal complex with definitely glandular 
 structures seems to shed upon its inherent tendencies in differ- 
 entiation, it must be in the intrinsic characters of the complex 
 itself that the solution of its problem is ultimately to be sought. 
 
 2. Evidence based on the gross morphology of the epiphyseal 
 
 complex 
 
 a. Phyletic constancy. If such evidence as may be obtained 
 from the gross morphology of the epiphyseal complex is taken 
 into account, a number of reasons may be advanced to show 
 that it is quite impossible to conceive of the pineal body as a 
 vestigial structure. These reasons seem so cogent as to place 
 upon the arguments which would refute them an unusually 
 heavy burden. 
 
204 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 The most significant feature with reference to the functional 
 activity of the pineal body appears to be the fact of its marked 
 phyletic constancy. Certainly, a structure which is marked for 
 regression or in which it is claimed that the evidences of regres- 
 sion may easily be found, would scarcely show such remarkable 
 tenacity throughout the phylum. Its occurrence in cyclostomes, 
 in all the fish, in amphibians and reptiles, in birds and mammals 
 reveals it as a structure which must have been called into being 
 in response to some definite demand, for why, otherwise, should 
 all of these classes of vertebrates so constantly present this 
 morphologic condition? 
 
 It is, perhaps, laying overmuch stress upon the phyletic 
 constancy of the epiphyseal complex to draw from these facts 
 alone the inference that it must be a physiologically active 
 organ. Its reported absence in the Myxinoids, in Torpedo 
 ocellata, and Torpedo marmorata as well as in Crocodilia would 
 seem to call into question the full value attached to the argu- 
 ment of its otherwise general constancy. On the other hand, it 
 must not be overlooked that in the history of the observations 
 devoted to the pineal body, a relatively large number of investi- 
 gators have reported the absence of the epiphysis in one form 
 or another, only to have their error corrected by subsequent 
 research and the presence of the organ clearly demonstrated. 
 By far the greater majority of observers in the morphology of 
 this portion of the brain are to-day of the opinion that the 
 epiphyseal complex as a whole or in some of its parts exists in 
 all vertebrates. It is certainly pertinent to the reported absence 
 of the organ in the forms mentioned to recall Kidd's 203 observa- 
 tion that the conditions in Torpedo need further review before 
 final acceptance of the statement that the epiphysis is absent in 
 these forms. The same also applies to Crocodilia, and until 
 this order has been more extensively examined, much reserva- 
 tion should be made in concluding that the pineal body is absent 
 in these reptiles. Again, Kidd's 203 contention with reference to 
 the Myxinoids adds another view which would render less serious 
 the reported absence of the epiphysis in the forms mentioned. 
 According to Kidd, it is not surprising that in Myxinoids the 
 
THE PINEAL BODY 205 
 
 epiphysis is wanting, since these are considered, by most author- 
 ities, as degenerated forms. 
 
 With these exceptions, then, so much in the minority, this 
 negative evidence should be accepted with much hesitancy. 
 In fact, the phyletic constancy of the epiphyseal complex is so 
 pronounced as to render the total absence of the organ in Myxi- 
 noids, Torpedo, and Crocodilia open to doubt. 
 
 b. Phyletic variations and morphologic specialization. If the 
 constancy already considered lends itself to the weight of evi- 
 dence in favor of the supposition that the pineal body is a func- 
 tional organ, then even more will the phyletic variations and 
 morphologic specializations which present themselves in this 
 organ support the view that the epiphysis is not a vestige, but 
 plays some physiologically definite role. 
 
 Certainly, when the marked specialization in the epiphyseal 
 complex in the various orders of vertebrates is taken into ac- 
 count, it is difficult to escape the conclusion that such modifica- 
 tions must have been in the interest of definite adaptations. 
 If these specializations referred to were indefinite or diffuse, it 
 might still be a question whether the processes were actually in 
 the interest of adaptation; but when, as is the case, form after 
 form shows such a high state of differentiation, such a definite and 
 discrete specialization, there seems to be little room for doubt 
 that a process of adaptation has been carried forward in order 
 to satisfy the demands for the development of specialized organs. 
 
 On the other hand, it cannot be denied that even such discrete 
 differentiation as the epiphyseal complex presents in many 
 forms, may represent but the rudiments of an adaptive process 
 which in some extinct forms, or perhaps even in some of the 
 proto- vertebrates, may have attained their functional consum- 
 mation only to impart an impulse in this direction to those verte- 
 brates which show the most definite specialization in the pineal 
 organs. 
 
 In this sense, all of the differentiation of the epiphyseal com- 
 plex throughout the vertebral phylum expresses an inherent 
 attempt to consummate the formation of organs which have 
 been essential in extinct forms or in the ancestors of the verte- 
 
206 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 brates. This contention, while it must have its place in the 
 discussion, seems to lose force in view of the special development 
 of the pineal organ in certain vertebrates. Thus, in cyclostomes 
 there is present, to a degree seen in no other vertebrates, a 
 development of the major constituents of the epiphyseal com- 
 plex. That is to say, both the pineal organ and parapineal 
 organ attain a degree of differentiation which at least justifies 
 the supposition that one, if not both of them have functional 
 activities of a visual nature. The presence in these forms of a 
 well-marked retinal structure, seen in the pineal organ as well 
 as in the parapineal organ, an end-vesicle containing a syncytial 
 structure comparable in many respects to the vitreous, a pig- 
 ment-free, ectal wall enclosing the end-vesicle and resembling a 
 lens, together with a bundle of nerve fibers connected with the 
 posterior commissure in the case of the pineal organ, and the 
 superior commissure in the case of the parapineal organ, con- 
 stitute irrefutable evidence of morphological specialization 
 adapting the organ to photo-receptive, if not visual purposes. 
 This supposition is further borne out by the fact that the organs 
 in their development grow rapidly away from the roof of the 
 brain and ultimately take up a position which, from its relation 
 to the surface of the body, affords certain epiphyseal structures 
 the best opportunity of becoming distance receptors. From the 
 striking position which the pineal and parapineal organs hold in 
 the vault of the skull, lodged as they are in a deep fossa, it would 
 seem evident that they have become so situated that they might 
 the more readily receive sensory impulses impinging upon the 
 surface of the head. 
 
 That this visual or photo-receptive tendency in the selachians, 
 ganoids, and teleosts should almost altogether disappear, al- 
 though the pineal organ itself remains as a conspicuous struc- 
 ture, would speak in favor of a pluripotentiality in the differen- 
 tiation of the epiphyseal complex. It is certain that in the 
 higher fish there is no evidence pointing to the development of 
 anything resembling the visual structures observed in cyclo- 
 stomes. In selachians the parapineal organ is entirely absent; 
 the pineal organ, on the other hand, is a large and prominent 
 
THE PINEAL BODY 207 
 
 structure presenting a proximal portion, a prolonged stalk, and 
 a fairly well marked end-vesicle. No tendency, however, is 
 observed toward the development of a photo-receptive appara- 
 tus. The thickened proximal portion communicates directly 
 with the ventricle on the one hand, and through the stalk with 
 the end- vesicle on the other. The fact that this latter portion 
 of the pineal organ is lodged in a deep fossa of the skull and thus 
 brought into close relation with the epidermis, would favor the 
 belief that in this structure may be observed the arrested or 
 abortive effort toward the formation of a physiological organ. 
 That this organ, however, deprived of the opportunity to reach 
 such a goal in its differentiation, should remain so prominent a 
 structure connected with the brain, would seem to refute the 
 conception that it is a mere vestige or rudiment; indeed, it 
 seems to compel the belief that it exists in the interest of some 
 other function as yet not entirely clear. 
 
 When, however, the finer histological structure of the pineal 
 organ in selachians is discussed, it may be possible to disclose 
 evidence which will at least suggest, that the structure in these 
 forms is functionally active. The point which the gross mor- 
 phological conditions in selachians does lay emphasis upon is the 
 presence of so prominent a structure, showing no evidence in 
 itself of retrogression and yet quite devoid of such specializa- 
 tion as would connect it definitely with visual function. 
 
 In the teleosts, the observation made with reference to the 
 selachians assumes even more importance, for here the pineal 
 organ shows a marked specialization which is entirely contrary 
 to the lines of differentiation followed in the development of a 
 visual organ. In most of the teleosts the pineal organ presents 
 a small proximal portion, a relatively short stalk, and a volumi- 
 nous thick-walled end-vesicle. The general follicular appear- 
 ance of the end-vesicle, together with its relatively large size 
 and the fact that it has neither migrated to such a great distance 
 from the roof-plate of the interbrain nor come to occupy a defi- 
 nite fossa in the vault of the skull, all go to disprove any inherent 
 tendency in the structure to differentiate as a visual organ. In 
 many teleosts a small parapineal organ develops, but never 
 
208 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 reaches dimensions comparable with the pineal organ. As in 
 the case of the selachians, the histology of the pineal organ of 
 the teleost will prove helpful in the interpretation of its function. 
 
 Thus, in the four great classes of fish, cyclostomes, selachians, 
 ganoids, and teleosts, the epiphyseal complex shows a remark- 
 able variation in its specialization, and while the tendency to 
 develop visual or photo-receptive structures is marked in the 
 cyclostomes, it is suspended, if not entirely absent, in selachians, 
 ganoids, and teleosts. 
 
 In the latter forms, however, the epiphyseal complex is so 
 conspicuous an element of the brain as to make the conclusion 
 that it is without function a difficult one to maintain. For these 
 reasons, it would seem justifiable to conclude that the epiphyseal 
 complex is pluripotential in its specialization and that while it 
 may be vested with the possibility of giving rise to a visual or 
 photo-receptive apparatus, it may and does become differ- 
 entiated as organs having some significance other than sensory. 
 
 Still greater modifications present themselves in the amphibia, 
 for in these forms the pineal organ shows an even more marked 
 differentiation than any of the other lower classes. The para- 
 pineal organ does not develop in urodela or anura. When, how- 
 ever, the structure of the pineal organ is considered, the fact 
 that it develops a proximal portion of such conspicuous dimen- 
 sions as to be secondary to the paraphysis in the roof of the 
 interbrain, from the free extremity of which there extends a thin 
 nerve filament connecting with an end-vesicle, it becomes clear 
 that the entire process of adaptation in this instance cannot be 
 in the interest of sensory function, for if that were the case, 
 why, then, should the proximal portion of the pineal organ 
 assume such conspicuity? 
 
 Stieda's 379 interpretation of the end- vesicle in amphibia as a 
 frontal subcutaneous gland is, of course, quite untenable, since 
 the end-vesicle manifests by its position and connections some 
 obvious adaptation to sensory activity. Yet to its proximal 
 portion might well be attributed a glandular function, not 
 only because of its unusually large dimensions, but also because 
 of the position which it holds with reference to the third ventricle. 
 
THE PINEAL BODY 209 
 
 If the argument bearing upon the pluripotentiality of specializa- 
 tion of the epiphyseal complex needed support or confirmation, 
 this is found in the conditions of amphibians. 
 
 The evidence afforded by the reptiles goes, perhaps, as far 
 as may be deemed necessary to confirm the pluripotentiality of 
 the pineal organ and its derivatives. In the ancient and primi- 
 tive reptiles, including the prosaurians and saurians, there is a 
 tendency for both pineal and parapineal organs to attain remark- 
 able development. But in these forms, it is the parapineal organ 
 which assumes predominance in' the development of a sensory 
 apparatus. In sphenodon and many of the lizards the parietal 
 or third eye reaches such a high state of differentiation as to 
 leave little doubt concerning its visual function. The well 
 marked optic vesicle, lodged in a parietal fossa and brought into 
 relation with the external epidermis by means of specialized cells, 
 affords incontrovertible evidence that this organ is adapted as a 
 distance receptor. The pineal organ, while it presents some 
 tendency towards the development of a visual organ, does, as a 
 matter of fact, fall far short of such attainment. Its end- vesicle 
 is smaller than in any of the other forms already considered. 
 Its stalk is shorter; on the other hand, its proximal portion has 
 assumed characters not as yet observed in the lower members of 
 the vertebrate series. So pronounced is the specialization of 
 this proximal portion that it needs no microscopic investigation 
 to disclose the marked differentiation of the structure. Its 
 walls are not only thick and convoluted, giving it a lobulated 
 appearance, but its diameters are greater than those of the 
 lower forms. 
 
 Upon passing to the more modern reptiles, including the 
 ophidians and chelonians, the tendency to specialization which 
 has previously been emphasized in this discussion, receives still 
 further accentuation. In these forms, the parapineal organ dis- 
 appears altogether and nothing remains to indicate that it ever 
 had existence in reptilia. There is no parietal fossa and no 
 specialization of the cutaneous surface in the head which might 
 even vaguely suggest the remnants of the parietal eye so con- 
 spicuous in the ancient reptiles. Yet, on the other hand, the 
 
 MEMOIR NO. 9 
 
210 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 pineal organ manifests such marked alterations as to leave no 
 doubt that a process of specialization is going on in this struc- 
 ture. It is a much more voluminous organ having a greater 
 solidity and presenting only one of the three fundamental por- 
 tions observed in the pineal organ of the lower forms. The 
 end- vesicle and the stalk of the end-vesicle have disappeared. 
 The proximal portion alone remains to represent the epiphyseal 
 complex. It also manifests certain modifications in its relation 
 to the brain, since now it no longer communicates with the ven- 
 tricle through a canal. Furthermore, it has developed a shallow 
 intermediate stem or stalk connecting it with the roof-plate. 
 
 The inception of the process resulting in the formation of 
 the pineal peduncle is first witnessed in the sphenodon and 
 lacertilia. The conditions in birds and mammals show a still 
 further tendency along the lines of specialization first manifested 
 in ophidians, for, as in these latter forms, neither the parapineal 
 organ nor the end-vesicle or stalk of the pineal organ makes its 
 appearance. The epiphysis in many of the birds becomes a 
 solid organ with no canal connecting it with the third ventricle, 
 although in certain birds this canal is present. In mammals the 
 canal has never been observed and the pineal body presents 
 itself as a dense, solid structure in close proximity to the roof of 
 the interbrain or resting upon the roof-plate of the midbrain. 
 
 Another observation made by Kidd 203 is pertinent in this con- 
 nection, to the effect that if nature is endeavoring to be rid of 
 the pineal body it has taken a remarkably long time imper- 
 fectly, if at all, to accomplish this end. The evidence that the 
 reptiles in the Palaeozoic era possessed a parietal eye is sub- 
 stantiated by the parietal foramen in these extinct forms, as 
 demonstrated by Bashford Dean. 82 
 
 All of this evidence concerning the phyletic variations and 
 morphologic specialization seems to justify the conclusion that 
 the epiphyseal complex is possessed of a pluripotentiality which 
 in a few forms has been realized as a more or less diffuse visual 
 structure, but which fundamentally appears to be in the interest 
 of a differentiation whose functionl significance is not sensory. 
 
THE PINEAL BODY 211 
 
 c. Relative constancy of the epiphyseal complex with reference 
 to other structures of the pineal region. The phyletic constancy 
 of the epiphyseal complex, when considered in conjunction with 
 the other derivatives of the diencephalic roof-plate, brings to 
 light a fact of no little significance. It has already been shown 
 how constant the epiphyseal complex, either in its entirety or 
 in some of its parts, is in the vertebrate phylum, and this be- 
 comes further emphasized by the fact that, this structure alone 
 of all the elements derived from the roof-plate presents such 
 undeniable constancy. If compared with one of the most con- 
 spicuous roof-plate derivatives, the paraphysis, the epiphyseal 
 complex stands out in marked contrast. The paraphysis is 
 present in its highest state of evolution in the middle of the 
 vertebrate series; that is to say, in amphibians and in older 
 reptiles. It is a conspicuous organ, showing but little differ- 
 entiation in cyclostomes and in fishes generally. In ophidians, 
 birds, and mammals it is absent. The inference which may be 
 drawn from these facts seems to be that the roof-plate of the 
 interbrain is capable of developing a structure which, when it no 
 longer subserves any purpose, ceases to exist. When the phy- 
 letic constancy of the epiphyseal complex is compared with that 
 of the paraphysis, it would seem evident that this very constancy 
 argues a demand on the part of the organ for the presence in the 
 animal of this complex or some of its parts. 
 
 To a less degree, the comparison in favor of the pineal organs 
 may be drawn with reference to the velum transversum, telen- 
 cephalic chorioid plexus, and dorsal arch. None of these show 
 such a marked tenacity as the epiphyseal complex, a fact which 
 but serves to emphasize the significance of the relative constancy 
 among the structures derived from the diencephalic roof-plate. 
 
 d. Relative constancy of the several parts of the epiphyseal com- 
 plex, with the predominance of the proximal portion. Since each 
 organ of the epiphyseal complex presents three more or less 
 well-defined portions, namely, the proximal portion, the stalk, 
 and the end- vesicle, it would be interesting to note the relative 
 constancy of the several parts in the phyletic series in order to 
 ascertain, if possible, which of these is the most fundamental 
 
212 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 element in the complex. Both organs are well developed in 
 cyclostomes. The proximal portion of the pineal organ, al- 
 though present, is not conspicuous, but it is doubtful whether 
 any structure which may be designated a proximal portion can 
 be discerned in the parapineal organ. The stalks and end- 
 vesicles are present and highly specialized. The stalks have 
 lost their original lumina and consist of two sets of nerve fibers. 
 Both end- vesicles are well differentiated. 
 
 In selachians the parapineal organ is entirely absent. The 
 proximal portion of the pineal organ is well marked, its stalk is 
 long and hollow, and its end- vesicle a dilated sac. 
 
 In ganoids and teleosts the parapineal organ is rudimentary; 
 in the embryo it presents a small proximal portion which subse- 
 quently becomes much reduced in size, rendering it difficult of 
 recognition in the adult. The stalk is short and slender and con- 
 tains no lumen. The end- vesicle is very small. The proximal 
 portion of the pineal organ shows a considerable dilatation and 
 is connected, by means of a hollow stalk, with an extensive 
 end-vesicle. 
 
 In amphibia the parapineal organ is absent. The proximal 
 portion of the pineal organ is a large, dilated sac whose lumen 
 communicates with the third ventricle. The stalk is reduced to 
 a slender nerve strand extending from the free extremity of 
 the proximal portion to the end-vesicle which lies immediately 
 beneath the skin in the region of the head. 
 
 In the primitive reptiles, including sphenodon and lacertilia, 
 the parapineal organ is present and shows a marked development. 
 In the embryo there is a prominent proximal portion, which, 
 however, becomes gradually reduced hi size, and in the adult is 
 difficult to distinguish. The stalk of the parapineal organ 
 presents itself in the form of a long slender fasciculus of nerve 
 fibers which connects the superior commissure with an end- 
 vesicle. The pineal organ shows a highly specialized proximal 
 portion which is large and convoluted. Its cavity communicates 
 with the third ventricle through a narrow canal. The stalk is 
 short and contains a cavity which communicates with the end- 
 vesicle at its distal extremity and also with the proximal por- 
 
THE PINEAL BODY 213 
 
 tion. In ophidians and chelonians the parapineal organ is 
 entirely absent, and the only element of the pineal organ which 
 persists is the proximal portion which has become converted into 
 a more or less solid structure extending from the roof of the brain 
 dorsad toward the vault of the skull. Similarly, in birds and 
 mammals, the only element of the epiphyseal complex which 
 may be recognized is the proximal portion of the pineal organ. 
 This, as in reptiles, is an organ of considerable density close to 
 the roof of the brain. 
 
 From these facts it will be seen that the proximal portion of 
 the pineal organ is the most constant element of the epiphyseal 
 complex, the next in point of frequency being the end-vesicle 
 and stalk of the pineal organ. It would seem, therefore, that the 
 proximal portion of the pineal organ should be considered the 
 fundamental element of the epiphyseal complex, and its struc- 
 ture would, therefore, demand particular attention. That this 
 element in the epiphyseal complex does show a marked tendency 
 toward specialization from the selachians to reptiles, birds and 
 mammals is convincing evidence that this structure is not to be 
 considered a vestige, for were such the case it would scarcely 
 manifest such a definite tendency toward specialization in the 
 processes of evolution. 
 
 e. The epiphy so-cerebral index. Not alone is the evidence 
 obtained from the comparative studies of the pineal body in 
 favor of its progressive specialization, but quite as much the 
 facts obtained from ontogenesis of the organ in man. We are 
 fortunate to possesss a careful series of observations made by 
 Cut ore 76 in which the weight of the brain as well as the weight 
 of the epiphysis and the hypophysis have been recorded. These 
 statistics are based upon the observations ranging from the new- 
 born to the seventieth year of life. In all, twenty-five brains 
 were studied, and it would seem that from such material, limited 
 though it may be, some light might be shed upon the ontogenetic 
 evolution, upon the epiphysis in its relation to the rest of the 
 brain and also to a recognized endocrinal organ, the hypophysis, 
 
 If, as has been frequently maintained, the pineal body is a 
 vestige and of no functional significance, then the tendency for 
 
214 
 
 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 this organ should be to manifest the signs of regression through 
 the periods of growth in man. Or if, on the other hand, as is 
 thought to be the case by many, the organ is functional only 
 in the fetal and in the early postnatal stages, then the relative 
 weight of the organ to the rest of the brain should show an 
 alteration in its ratio, indicating a progressive retrograde process 
 taking place in its structural elements. 
 
 In preparing the figures of Cutore, in order most effectively to 
 assemble the facts necessary to this argument, his cases were 
 grouped in such a way as to constitute five more or less well- 
 defined epochs of life. 
 
 1. Six examples of infants in the first year. 
 
 2. Five examples of infants in the second year. 
 
 3. Six examples of children from 3 to 14 years. 
 
 4. Five examples of adults from 15 to 25 years. 
 
 5. Three examples of adults from 60 to 70 years. 
 
 AVERAGE WEIGHT IN GRAMS 
 
 INDEX TO BRAIN 
 
 Epoch 
 
 Brain 
 
 Hypophysis 
 
 Epiphysis 
 
 Hypophysis 
 
 Epiphysis 
 
 1st 
 
 600 
 
 0.103 
 
 0.031 
 
 0.00017 
 
 0.00005 
 
 2nd 
 
 734 
 
 0.154 
 
 0.055 
 
 0.407 
 
 0.00007 
 
 3rd 
 
 1,105 
 
 0.262 
 
 0.100 
 
 0.00024 
 
 0.00009 
 
 4th 
 
 1,218 
 
 0.508 
 
 0.119 
 
 0.00040 
 
 0.00009 
 
 5th 
 
 1,125 
 
 0.500 
 
 0.130 
 
 0.00040 
 
 0.00010 
 
 It will be seen from these figures that of the "three structures, 
 considered, the average weight of the epiphysis alone tends to 
 increase constantly through the five epochs differentiated in 
 this study. The brain itself shows a constant increment in 
 weight from the first year to and through the twenty-fifth year, 
 but in the fifth epoch, from sixty to seventy years, there is an 
 apparent decrease of nearly 100 grams in brain weight. The 
 increase in the hypophysis runs parallel to that of the brain, 
 for up to the fourth epoch and including it the increment in 
 weight in the hypophysis is constant, but in 'the fifth epoch, 
 from sixty to seventy years, the figures seem to indicate a defi- 
 nite decrease in weight. The indices expressing the epiphyso- 
 
THE PINEAL BODY 215 
 
 cerebral and hypophyso-cerebral ratio bear out this observa- 
 tion and definitely indicate an increase in the proportion between 
 the brain and the epiphysis from the first year of life to the 
 fifth epoch, between sixty and seventy years. If compared with 
 the conditions observed in a definitely known endocrinic organ, 
 the hypophysis, it will be observed that in the first period the 
 weight of the pineal bcdy is 30 per cent of the hypophysis; in 
 the second epoch it is also 30 per cent; in the third epoch it is 
 35 per cent, an increase which is of much importance and inter- 
 est in this connection, since it is the general supposition that the 
 gland has its greatest functional activity during this time of 
 life. In the fourth epoch the epiphysis is 22 per cent of the hypo- 
 physeal weight, while in the fifth epoch it is 25 per cent. 
 
 It should be borne in mind, while considering these figures , 
 that the hypophysis is a compound organ, being made up of a 
 neural portion in addition to an element derived from the oral 
 ectoderm. Its greater weight, therefore, is in part, at least, 
 explained by its non-glandular neural portion, and its total 
 glandular weight would be represented by a fraction only of this, 
 total. In this light, the proportion between the epiphysis and 
 the hypophysis would be materially changed, and while it is 
 impossible to say exactly what ratio the neural portion of the 
 hypophysis bears to the glandular portion, it would be safe to 
 assume that the proportion is as 1:2. 
 
 From this standpoint, the figures concerning the epiphysis 
 assume more definite significance and would seem to point 
 strongly to the supposition that an organ destined to become 
 regressive would scarcely keep pace so constantly in its weight 
 increment with an organ like the hypophysis of known endo- 
 crinic function. The figures cited are suggestive in another 
 sense, namely, they would seem to show that the activity of the 
 pineal organ, should such be accredited to it, does not cease at 
 any particular period of life, and that while there may be reason 
 to believe that the greatest functional activity is present in the 
 third epoch, between the third and fifteenth years, there are 
 good reasons to believe that the organ does not cease to perform 
 its functions even up to the time of old age. 
 
216 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 /. Resistance to the encroachment of the corpus callosum. An- 
 other characteristic in the ontogenesis of the epiphysis, especially 
 in mammals, speaks against the possibility of its being a vestige 
 and indicates in it a tenacity as a morphologic structure so 
 marked as to suggest the probability of some inherent functional 
 activity. With the advent of the commissural fibers whose mas- 
 sive collection goes to make up the corpus callosum, the mam- 
 malian brain takes on a character not observed in the lower 
 forms. The gradual extent of this great 'interhemispheral com- 
 missure in a caudal direction subjects the entire roof of the 
 diencephalon to new conditions. The influence of these new 
 conditions is readily seen in the flattening of the dorsal sac and 
 the reduction of the paraphyseal arch. Yet, even in the in- 
 stances in which the corpus callosum extends far enough caudad 
 to reach the midbrain, the epiphysis withstands its. encroach- 
 ment and gives evidence of a resistive adaptation against the 
 pressure of the new structure. It seems fair to presume that if 
 there were vested in the pineal body an inherent tendency to 
 retrograde, under the pressure of this newly developed mam- 
 malian structure which has so uniformly altered the configura- 
 tion of other elements in the diencephalic roof-plate, the epiphysis 
 itself must have given evidence of much less resistance or per- 
 haps have Succumbed altogether. Its evident effort at adapta- 
 tion has already been referred to in the classification of the 
 epiphysis in mammals which, according to Cutore, 76 shows a 
 disposition on the part of the organ to accommodate itself to 
 the presence of the corpus callosum, in some forms being retro- 
 callosal in position, in others supracallosal, and still again main- 
 taining itself in all its morphologic intactness in a distinctly 
 subcallosal position. 
 
 If the epiphysis is to be considered a vestige, in view of the 
 morphologic evidence above summarized, it seems apparent 
 that the burden of proof rests with those making the claim that 
 it is a rudimentary structure. To maintain this position they 
 must meet with some well-sustained objections the following 
 established facts: 
 
THE PINEAL BODY 217 
 
 1. The phyletic constancy of the epiphysis. 
 
 2. Its phyletic variations and morphologic specializations. 
 
 3. Its relatively greater phyletic constancy with reference to 
 other structures in the pineal region. 
 
 4. The phyletic predominance of the proximal portion of the 
 pineal organ. 
 
 5. The evidence of its progressive specialization in ophidians, 
 birds, and mammals. 
 
 6. The increase of the epiphy so-cerebral index from the 
 earliest stages to the latest periods of life in man. 
 
 7. The resistance to the encroachment of a prominent neo- 
 morph in the mammalian brain such as is the corpus callosum, 
 whose presence has produced such a marked alteration in the 
 other constitutents of the diencephalic roof-plate. 
 
 3. Evidence based on the 'histology of the epiphy seal complex 
 
 From the comparative histology of the epiphyseal complex, 
 it becomes evident that specialization in these organs has fol- 
 lowed two main lines: First, the structures have either differ- 
 entiated in the interest of forming visual organs or, second, 
 they have given rise to glandular itissue. In some instances, 
 both of these tendencies may be observed, that is to say, in 
 certain species the differentiation has been in the interest of 
 visual apparatus in one part of the epiphyseal complex, while in 
 another part, distinct glandular tendencies are apparent. It 
 seems advisable for the purpose of obtaining as comprehensive a 
 view as possible of the histology of this portion of the brain to 
 consider the leading features of the finer structure in the pineal 
 body of each of the classes of vertebrates. 
 
 Histological evidence in cyclostomes. The striking histological 
 features in cyclostomes are the specializations in both pineal and 
 parapineal organs in the interest of forming visual structures. 
 The end-vesicle of the parapineal as well as the pineal organ 
 presents a retina. This structure in the pineal organ contains 
 cells of a distinct rod-like shape which have, therefore, been 
 designated the rod cells. Other cellular elements are also .ob- 
 
218 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 served in the ventral wall of the end-vesicle which appear to be 
 of a sensory nature. Certain large elements have been recog- 
 nized in the deeper layers of the tissue and by some authorities 
 are considered to be ganglionic cells. In addition, there are cells 
 of an ependymal nature or modifications of the latter which give 
 the impression of neuroglia tissue. There can 'be little question 
 that the retina of this organ is well enough defined to deserve 
 that designation. Whether it is actually functional as a visual 
 organ is not altogether clear, for the relation of the pineal eye in 
 cyclostomes to the surface of the head does not afford the most 
 advantageous conditions for a distance receptor. 
 
 The end-vesicle of the parapineal organ closely resembles the 
 finer structure in the corresponding part of the pineal organ. 
 There are, however, certain differences which are more those of 
 degree than of kind. The rod cells, such conspicuous elements 
 in the pineal organ, are less well defined in the parapineal organ 
 and so also are the ganglionic cells. 
 
 The differentiation of the dorsal wall of the end-vesicle in the 
 pineal as well as in the parapineal organ 'manifests a tendency 
 toward lens formation, for in both cases the cells in this region 
 are entirely pigment-free and give rise to a translucent structure 
 known as the pellucida. ' Further evidence of the visual adapta- 
 tion observed in the end-vesicle of the two structures of the 
 epiphyseal complex is the fact that the cavity of the vesicle is 
 filled with a coagulum in the meshes of a delicate syncytium, a 
 structure which so closely resembles a primitive vitreous that it 
 may be regarded as analogous, if not homologous to that struc- 
 ture. The presence in the retina of a widely distributed white 
 pigment lends the necessary opacity to the visual membrane. 
 Both end-vesicles contain this pigment; its presence serves 
 further to convey the impression of differentiation along visual 
 lines. 
 
 The stalks of both the pineal and parapineal organs bear a 
 certain amount of confirmatory evidence in favor of the belief 
 that the epiphyseal complex in cyclostomes has made the at- 
 tempt at visual adaptation. Nerve fibers are uniformly ob- 
 
THE PINEAL BODY 219 
 
 served in the stalks; those coming from the pineal end-vesicle 
 terminate in the posterior commissure, while those seemingly in 
 connection with the parapineal end-vesicle end in the habenular 
 commissure. Some collateral evidence is afforded by the appear- 
 ance of a parietal cornea, a fiberless tissue which surrounds the 
 pineal and parapineal end-vesicles. 
 
 All of these histological facts, based upon the observation of 
 cyclostomes, indicate what may be considered an abortive yet 
 a well-advanced attempt to the formation of two eyes. There 
 is no evidence of glandular formation in any part of the epi- 
 physeal complex in cyclostomes. 
 
 Histological evidence in selachians. The characteristics of finer 
 structures, so conspicuous in petromyzon and its congeners, is 
 strikingly absent in the next higher order, the selachians. In 
 consequence of the apparent lack of differentiation, the entire 
 parapineal organ is absent, while the pineal organ, although 
 conspicuous for its size, shows no tendency toward the formation 
 of a retina, pellucida, white pigment, or nerve fibers. It is a 
 question whether the pineal organ in selachians should be con- 
 sidered as a primitive organ or as one in a stage of retrogression. 
 The walls of the end-vesicle are made up exclusively of epen- 
 dymal cells and contain neither spindle nor rod cells. In one 
 form, Scyllium, Galeotti 140 described a peculiar appearance of 
 the cells of the end-vesicle which seemed to indicate a secretory 
 function. This conclusion of Galeotti's depends on the appear- 
 ance of fuchsinophile granules not only in the nuclei of the cells, 
 but scattered diffusely throughout the cytoplasm. Studnicka 391 
 also recognized these cells and, while he was unwilling to attrib- 
 ute any definite function to them, he was of the opinion that they 
 could not be secretory in their nature. 
 
 It is apparent, therefore, in passing from the cyclostomes to 
 the selachians that there is a striking absence of any visual 
 differentiation or any tendency in this direction, while the 
 presence of certain histological characters in the cells furnishes 
 evidence pointing to a possible glandular formation in the end- 
 vesicle of the pineal organ. 
 
220 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Histological evidence in ganoids. The pineal organ alone 
 develops in ganoids, although in a single form, namely, Amia, 
 an abortive parapineal organ makes its appearance. The end- 
 vesicle of the pineal organ in ganoids generally shows some 
 tendency toward the development of a retinal or pellucidal 
 layer, although neither of these is well marked. Studnicka, 391 
 as the result of his studies upon ganoids, does not believe that 
 there is any evidence of glandular activity in the end-vesicle 
 or proximal portion which is at all comparable to that of the 
 corresponding parts in selachians. On the other hand, he does 
 not deny that there may possibly be secretory function in the 
 pineal organ of ganoids. 
 
 Histological evidence in teleosts. The epiphyseal complex in 
 teleosts differs from that in selachians and ganoids in being a 
 much larger structure. The end-vesicle, furthermore, mani- 
 fests, in nearly every species, a pronounced tendency toward the 
 convolution of its walls. Not only is this process apparent 
 upon the surface, but section of the vesicle shows it to consist 
 of many folds and diverticula, all of which give to it the appear- 
 ance of a tubular gland in communication with the third ven- 
 tricle by means of a long hollow stalk. Galeotti 140 in Leuciscus 
 found evidence of secretory activity in the presence of fuch- 
 sinophile granules similar to those described by him in selach- 
 ians. The product of this secretion, he thinks, is delivered to 
 the lumen of the end-vesicle and thus to the ventricle of the 
 diencephalon. Studnicka 391 observed cells having a similar 
 appearance, and although he did not commit himself definitely 
 as to their nature, he nevertheless expressed the belief that the 
 organ is not entirely a gland. Some nerve fibers of the stalk 
 seem to represent a rudimentary pineal nerve. 
 
 Histological evidence in amphibia. The first recognition and 
 description given by Stieda 379 in which he called the end-vesicle 
 a frontal subcutaneous gland was evidently a misinterpretation 
 of the conditions in amphibia. The end- vesicle in these animals 
 is fairly well developed, presenting a retina and lens which, 
 although clearly recognizable as such, have attained scarcely 
 more than an abortive state in their development. A long 
 
THE PINEAL BODY 221 
 
 slender stalk made up almost exclusively of nerve fibers con- 
 nects this organ with the tip of the proximal portion arid con- 
 stitutes a nervus pinealis, in the strict sense, which terminates in 
 the posterior commissure. Galeotti 140 in Spelerpes fuscus 
 observed evidence of secretory activity, and this he also found in 
 Bufo and Rana. The evidence of secretory activity depended 
 upon the appearance of fuchsinophile granules in the cytoplasm. 
 'Studnicka, 391 following Galeotti, found, as he had previously 
 observed in selachians and teleosts, many cells in adult amphibia 
 containing cytoplasmic granules. These he interpreted as cells 
 having a sensory nature. Galeotti based his belief of secretory 
 activity in the pineal organ not merely upon the presence of 
 fuchsinophile granules, but quite as much upon epithelial char- 
 acters of the cells which were arranged in alveoli, thus giving 
 the end- vesicle and the proximal portion a glandular appearance. 
 
 It is apparent from this evidence that amphibia in general 
 present a very abortive attempt toward the formation of retinal 
 and lenticular structures, while the end-vesicle and the proximal 
 portion of the pineal organ both show some evidence of glandu- 
 lar formation. 
 
 Histological evidence in reptilia. The finer structure of the 
 epiphyseal complex in the primitive reptiles, including Spheno- 
 don and lacertilia, shows that in these forms the parapineal 
 organ attains its highest differentiation as a visual structure. 
 The pineal organ, however, shows no tendency whatsoever in 
 this direction, while, on the other hand, its proximal portion 
 affords many indications that its differentiation has been along 
 glandular lines. In ophidia and chelonia the proximal por- 
 tion of the pineal organ alone persists and has the appearance 
 of a highly vascular, richly branched, tubular gland. The 
 structure generally known as the pareital eye is a prominent 
 morphological feature in primitive forms of reptiles. It is 
 absent in certain geckonidae and in a number of agamidae. It 
 attains its greatest differentiation in Sphenodon and here pre- 
 sents a well marked retina, lens, vitreous, cornea, and nerve, the 
 latter relating to the ganglion habenulae. The accessory struc- 
 tures related to the parietal eye, including the cornea, parietal 
 
222 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 fossa, and parietal spot, all give evidence of the most complete 
 adaptation for visual function. 
 
 Studnicka 391 believes that the rich capillary blood supply in 
 ophidia speaks in favor of the glandular nature of the organ, 
 its secretion being contributed to the blood stream. In chelonia 
 the cellular elements are mostly ependymal and neurogliar and 
 no nerve cells or nerve elements are found. There is, however, 
 no clear evidence of the secretory nature of the epiphyseal com-' 
 plex in these forms. 
 
 The conclusions which may be drawn with reference to reptiles 
 seem to indicate that in the primitive forms the parapineal organ 
 assumes the highest differentiation which it attains as a visual 
 structure. There is some evidence that the pineal organ, even 
 in the animals, manifests a tendency toward glandular forma- 
 tion. In ophidians, however, there can scarcely be a doubt 
 that the proximal portion of the pineal organ is the only element 
 which persists and that it has a definitely glandular structure. 
 This is probably true also in chelonians. The pineal gland in the 
 snake and turtle probably contributes its secretion to the blood 
 stream, but may also impart a portion of it to the cerebrospinal 
 fluid. The more recent reptiles manifest no disposition on the 
 part of the epiphyseal complex to develop any sensory or other 
 type of neural mechanism. 
 
 Histological evidence in birds. The conspicuous change in the 
 epiphyseal complex noted in the transition from the primitive 
 reptiles to those of more recent history is strikingly emphasized 
 when the condition's in this region of the brain in birds are 
 reviewed. Here, as in the snakes and turtles, there is com- 
 plete suppression of the parapineal organ, and that tendency 
 toward the differentiation of a visual apparatus which seems to 
 have reached its height in Sphenodon, has so far receded as to 
 leave no indication in birds of its earlier existence. This histo- 
 logical feature of itself is highly significant, but when taken in 
 conjunction with the appearance offered by the finer structure of 
 the pineal body in birds, it seems to set all doubt aside as to the 
 inherent tendency of the epiphyseal complex along its major 
 lines of differentiation. In every species of birds which has so 
 
THE PINEAL BODY 223 
 
 far come under observation, the differentiation in the pineal 
 body has been in the interest of glandular formation. This 
 evidence is not alone to be found in the character of the cells 
 which compose the body, but even more in the arrangement of 
 these cells whose alveolar patterns constitute irrefutable reasons 
 for regarding the epiphysis as a true gland in birds. 
 
 Three types of this gland are found in the avian forms, namely, 
 1) the tubular type, in which the secretion is delivered to the 
 ventricular system; 2) the endocrinic type, in which the secre- 
 tion reaches the blood stream, and 3), a mixed type, partaking 
 of the character of each of the former varieties. This evidence 
 afforded by birds is so conclusively in favor of the glandular 
 nature of the epiphysis as to leave no grounds for dispute. 
 
 Histological evidence in mammals. It is perhaps in mammals 
 that the most extensive observations have been made with 
 reference to the histology of the pineal body. Indeed, it is in 
 these animals that the greatest variety of opinion has been 
 expressed. It would seem advisable to take into account these 
 different views concerning the histological character of the organ. 
 A large group of investigators adheres to the belief that the 
 pineal body is a blood vascular gland. This group includes, 
 among others, Valentin, 403 Faivre, 114 Leydig, 231 Bizzozero, 31 
 Galeotti, 140 Constantini, 71 Cutore, 76 Galasescu-Urechia, 137 
 Krabbe, 217 Biondi, 49 and Kidd. 203 Jordan, 199 although he does 
 not advocate the improbability of glandular formation, believes 
 that the organ is essentially neural in its structure. 
 
 Several investigators maintain that the epiphysis in mammals 
 consists exclusively of neuroglia. Among these are Cionini, 66 
 Edinger, 103 and Weigert. 418 Mihalkovicz 274 believed that the 
 cellular consistency of the pineal body in mammals was exclu- 
 sively of the ependymal type. Those of another group assert 
 that the epiphysis resembles a lymph gland. Of this opinion are 
 Schwalbe, 348 Henle, 171 Ellenberger 110 Mingazzini, 276 and Lord. 249 
 
 Although it has been frequently claimed by many writers 
 among both the early and recent workers in this field that the 
 epiphysis is a vestige, it is interesting to note that no suggestion 
 of such a possibility is made by any of the authorities just 
 
224 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 cited. This is of particular significance because this list in- 
 cludes the names of those who have given the most extensive 
 attention to the histological character of the epiphysis in 
 mammals. Milhalkovicz' 274 conception of the histology of the 
 pineal body seems hardly tenable, for it requires little study 
 covering a number of different mammalian forms to become con- 
 vinced that the cellular elements entering into the epiphysis 
 have nothing in common with the ependymal cells. Even 
 though it may be admitted that a certain number of the cellular 
 constituents of the epiphysis are ependymal in type, it cannot, 
 in the light of our present knowledge, be held that the organ is 
 made up exclusively of this type of cells. 
 
 On the other hand, it 13 not possible to acceed to the conten- 
 tion of those who uphold the idea that the epiphysis is similar 
 to lymphatic glands. Not only does the character of the chief 
 cellular elements in the pineal body of mammals make this 
 position seem untenable, but even more does the arrangement 
 of these cells point away from the supposition that this is in 
 any sense lymphoid in character. Few cells in the body are 
 more conspicuous for their histological character than the chief 
 or parenchymatous elements of the mammalian epiphysis. 
 The large and centrally placed nucleus, the extensive and glan- 
 dular cytoplasm mark these cells so definitely that they may be 
 recognized without any difficulty even in those instances when 
 they become ectopic because of such migration as not infre- 
 quently results from tumor formation in the pineal body. 
 
 Our own work in this regard is illustrated in the figures which 
 show the character of the pineal gland cells in Macropus grayi, 
 Zalophus, Camelus dromedarius, Capra hylocrius, Lepus, Simia 
 satyrus, and in man. Furthermore, our observations in the 
 ontogenesis of the epiphysis in Felis domestica and in man, 
 illustrations of which are given in figures 91 and 92, show that 
 in the early stages of differentiation the nuclei of the ependymal 
 cells are so large and the cytoplasm so scanty that they give 
 the impression of lymphoid tissue, but in the later stages the 
 cytoplasm increases so considerably in amount that it is no 
 longer possible to conceive of these cells as lymphoid in char- 
 
THE PINEAL BODY 225 
 
 acter. In fact, they have in the later periods of fetal and early 
 postnatal life all the appearances usually associated with glan- 
 dular cells. As compared to the cells in the glandular portion 
 of the hypophysis, the size of the pineal cells is two or three 
 times as great. This difference in size affords a striking point 
 of differentiation in those pathological conditions in which the 
 pineal cells in the course of tumor formation have migrated into 
 and through the posterior lobe of the hypophysis and invaded 
 the pituitary gland. The contrast is so marked as to present 
 no difficulty in the identification of the two varieties of cells. 
 That the epiphysis is made up of neuroglia cells in large part, 
 if not entirely, has been the contention of several observers. 
 The presence of short, branching fibers in close proximity to the 
 pineal cells has seemed to be the basis for this. On the other 
 hand, if the pineal cells in mammals are to be regarded as neu- 
 roglia, it must be granted that they are certainly unlike the 
 neuroglia cells observed hi other parts of the central nervous 
 system. Dimitrova, 92 who makes out such a strong case from 
 her histological study in favor of the neuroglial character of the 
 epiphysis, seems to base her conclusions upon criteria which are 
 not wholly convincing, for the mere presence of demonstrable 
 fibers in the neighborhood of the cells does not of itself indicate 
 that these cells are neuroglial in character. Furthermore, this 
 view neglects to take into account the highly specialized char- 
 acter of the pineal cells. If, on the other hand, it be granted 
 that the cell constituency of the epiphysis is, in major part, 
 neurogliar, this admission would not wholly invalidate the idea 
 that the structure is glandular in nature, for, according to the 
 most recent researches of Nageotte 281 and Ma was, 263 neuroglia 
 cells contain mitochondria and hence, according to these inves- 
 tigators, should be considered as glandular elements. In this 
 light, the neuroglia throughout the entire nervous system is 
 endowed with secretory function. In general, however, it 
 does not seem necessary to invoke this interpretation of the 
 neuroglia in order to place the pineal body in the class of glan- 
 dular structures, for the character of the pineal cells is in itself 
 sufficient argument in favor of a function different from that 
 
 MEMOIR NO. 
 
226 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 attributed to neuroglia in the ordinary sense and most in favor 
 of a glandular activity. 
 
 The observations of Nicolas, 283A later confirmed by Dimitrova, 92 
 in which muscle cells were reported as histological elements of 
 the epiphysis in several Ungulates, have not been confirmed by 
 any other observers, and some authorities have been categorical 
 in their affirmation concerning the absence of such elements. 
 That the epiphysis may contain nerve cells and nerve fibers is 
 probable, but there is no evidence in mammals of the existence 
 of any neural mechanism in the pineal body. 
 
 To consider the epiphysis in mammalia as a vestige in the 
 light of the histological evidence here summarized seems to be 
 an attitude which is wholly untenable, all the more so when 
 this histological evidence points to the fact that the structure 
 is a gland. For in this respect not only is the character of the 
 cells significant, but their arrangement in definite acini, the rich 
 vascular network about these acini, and the trabeculation by 
 means of connective tissue which gives this structure the appear- 
 ance common to all glands, are also suggestive of this fact. 
 
 The final conclusion to be drawn from the histological evidence 
 in the epiphyseal complex of vertebrates would seem clearly to 
 indicate that this structure of the pineal region possesses a 
 pluripotentiality whose fundamental, inherent tendency is in 
 the interest of glandular differentiation and that in a few in- 
 stances, as in cyclostomes, amphibia, and in primitive reptiles, 
 the parapineal or pineal organ may become further differentiated 
 in the interest of a highly specialized sensory mechanism which 
 has, or has had, visual function. 
 
 4. The relation of the parietal eye to the pineal body 
 
 Much of the difficulty in interpreting the relation between 
 the parietal eye and pineal body arises from a confusion in the 
 use of terms. If by pineal body is meant the epiphysis as it 
 appears in mammals, it becomes relatively simple to discuss 
 the relation between this structure and the third eye of verte- 
 brates. It may perhaps be arbitrary thus to limit a term which 
 

 THE PINEAL BODY 227 
 
 has not always been restricted to the sense here advocated, and 
 yet, as has been previously pointed out, it was from precisely 
 the conditions in mammals that the descriptive conception, 
 pineal body, took origin. 
 
 The theory that the pineal body is the vestige of the parietal 
 eye is accepted by many. According to this view, the third 
 eye of vertebrates should be regarded as primordial and the 
 pineal body an arrested development in the attempt to reach 
 such differentiation. The evidence, however, is by no means 
 conclusive, for, as has previously been shown, the entire epi- 
 physeal complex springs from a region which is fundamentally 
 glandiferous, while only in a very few instances is a tendency 
 toward sensory differentiation recognizable in it. By far the 
 great majority of vertebrates manifest in the epiphyseal complex 
 no tendency whatsoever toward the development of any neural 
 mechanism. This would seem to indicate that the tendency for 
 the epiphyseal complex to develop visual structures is a secon- 
 dary and not a primordial character. Furthermore, if the 
 pineal body was in any true sense the vestige of the parietal 
 eye, it would seem almost inevitable that the organ should con- 
 tain remnants indicative of visual specialization. The absence 
 of such evidence at least raises a reasonable doubt that the pineal 
 body had at any time possessed visual function. The almost 
 universal absence of true ganglionic cells as well as the lack of 
 nerve fibers, which may be regarded as belonging to some cate- 
 gory other than those of the sympathetic system, would seem to 
 call into- question the possibility of the pineal body ever having 
 participated in the formation of a neural mechanism. This may 
 be considered negative evidence. There remains to be men- 
 tioned, however, the significant fact that the pineal body in all 
 of the higher vertebrates manifests a tendency to differentiate 
 along lines which cannot be interpreted as in the interests of 
 visual function. As has been previously shown, the differen- 
 tiation which does occur in the higher reptiles, birds, and mam- 
 mals gives rise to glandular tissue. From these facts it seems 
 possible to conclude that the pineal body is not a vestige of the 
 parietal eye. 
 
228 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 The supposition advanced by Hertwig 175 and others that the 
 pineal process in birds and mammals undergoes metamorphoses 
 which give rise to an organ of a glandular or follicular structure 
 has little to support it. Peytoureau 308B maintained that in 
 the evolution through the vertebrate phylum the pineal body 
 has become partly atrophic and partly metamorphosed in such 
 a way as to cause a modification in the connection with the 
 nerve centers. Ultimately, it has taken on the characters of 
 an epithelial organ, in fact, a highly vascular gland represented 
 in the higher mammals by the pineal gland and its peduncle. 
 To assume that an actual process of metamorphosis, in a literal 
 sense, from a visual organ to a glandular structure, is respon- 
 sible for the differences between the parietal eye and the pineal 
 gland seems wholly unsatisfactory. If, however, this view has 
 reference to a deflection in the ontogenetic process, as a result of 
 which the pineal anlage in certain forms, instead of giving rise to 
 a visual structure, produces a gland, there may be some justifi- 
 cation of ascribing these changes to metamorphosis. Yet, even 
 in this sense, to attribute the differences between the parietal 
 eye of Sphenodon and the pineal gland of the bird to such an 
 indefinite process of alteration does little more than apply a 
 term to the process without offering an explanation for it. 
 
 Certain investigators, among them Rabl-Ruckhard, 322 Ahl- 
 born, 2 and Spencer, 368 regard the pineal body as an unpaired 
 parietal eye which, in many classes, for example, reptiles, appears 
 to be tolerably well preserved, but in most vertebrates is in a 
 process of degeneration. This theory goes a step further than 
 that which regards the pineal body as a vestige. According to 
 the former view, the pineal differences between such forms as 
 possess a parietal eye and those in which no such structure 
 develops are attributed to a process of degeneration, while, the 
 latter theory ascribes them to an arrested development. Evi- 
 dence of degeneration in the higher vertebrates is difficult to 
 discern. The figures already cited in reference to the human 
 pineal gland (p. 158) makes it hard to believe that a retrograde 
 process is present, even in the late periods of life. The appear- 
 ance of brain sand in itself is not sufficient to justify such a con- 
 
THE PINEAL BODY 229 
 
 elusion. Furthermore, in no instance is there the slightest 
 indication that the pineal body in the higher vertebrates con- 
 tains histological elements which may, in any sense, be regarded 
 as degenerated products of the visual structures in the parietal 
 eye. That the pineal body in birds and mammals may be inter- 
 preted as the result of a degenerative process affecting the 
 parietal eye seems wholly untenable in the absence of any con- 
 vincing signs of such degeneration and also because the weight 
 of evidence furnished by many facts indicates 'the glandular 
 nature of the organ. 
 
 It is interesting in this connection to give the opinion of 
 Bashford Dean, 83 in which that author expresses doubt concern- 
 ing the connection between the epiphysis and the median eye of 
 vertebrates. 
 
 The evidence as to the presence primitively of a median eye in fishes 
 is certainly far from satisfactory. It is possible that fishes and am- 
 phibia may in their extant forms have lost all definite traces of this 
 ancestral (visual) organ on account of some peculiar conditions of their 
 aquatic living. On this supposition evidence of its presence might be 
 sought in the pineal structures of the earliest palaeozoic fishes, whose 
 terrestrial kindred and probable descendants may alone have retained 
 the living conditions which fostered its functional survival. It is of 
 interest, accordingly, to find that in a number of fossil fishes the pineal 
 region retains an outward median opening whose shape and position 
 suggest that it may have contained an optic capsule. If the median 
 eye existed in these forms it may well have been passed along in the 
 line of descent through the early amphibia (where substantial traces 
 of a parietal foramen occur, e.g. Cricotus) to the ancestral reptiles. 
 
 The evidence that the median opening in the head-shields of ancient 
 fishes actually enclosed a pineal eye is now felt by the present writer 
 to be more than questionable. The remarkable pineal funnel of the 
 Devonian Dinichthys is evidently to be compared with the median 
 foramen of Ctenodus and Palaedophus, but this can no longer be looked 
 upon as having possessed an optic function, and thus practically renders 
 worthless all the evidence of a median eye presented by fossil fishes. 
 
 It must, for the present, be concluded accordingly that the pineal 
 structures of true fishes do not tend to confirm the theory that the 
 epiphysis of the ancestral vertebrates was connected with a median 
 unpaired eye. More probably it was connected with the inner vation 
 of the sensory canals of the head. 
 
 The theory that the epiphysis in the true fishes is connected 
 with the innervation of the sensory canals of the head adds a 
 
230 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 new interpretation concerning the function of the pineal organ. 
 It is not our purpose to discuss this hypothesis, but we do desire 
 to emphasize the improbability of the pineal body in higher 
 vertebrates being the vestige of any neural mechanism. This 
 opinion is based on the general absence of definitely neural 
 elements in the pineal gland other than those connected with the 
 sympathetic system. 
 
 Terry 392 in Opsanus could find no evidence to support Dean's 
 supposition that the epiphysis of true fishes is connected with 
 the innervation of the sensory canals of the head. He was, 
 moreover, unable to discover the evidence in the teleost to sup- 
 port the theory that the pineal body is an ocular organ either 
 degenerate or rudimentary. 
 
 The portion of the epiphyseal complex which becomes special- 
 ized as the eye-like structure of the lower vertebrates constitutes 
 the end-vesicle. This end-sac may be part of the pineal or of 
 the parapineal organ, depending upon the form in which it 
 occurs. In every instance the appearance of visual element j is 
 limited to the end-vesicle. Not only is the structure notable 
 for the eye-like character of its histological elements, but it 
 occupies a position with reference to the brain and also to the 
 skull which further serves to distinguish it. Its connection with 
 the 'roof of the interbrain is by means of an attenuated stalk, 
 which gives the entire structure the appearance of a long append- 
 age of the brain. The junction of the stalk with the roof is 
 usually not a direct one since the connection in most forms is 
 accomplished through the proximal portion. These several 
 parts, which may be recognized in the pineal and parapineal 
 organs of certain classes, should be regarded as separate mor- 
 phologic entities. The proximal portion has little in common 
 with the end-vesicle. Its position and histological characters 
 mark it as strikingly different. Its only actual relation with 
 the vesicle is one of continuity through the stalk. This con- 
 tinuity may, in some cases, be almost lost or maintained only 
 by a small filament of nerve fibers. Such, for example, is the 
 condition in amphibia, a class which, perhaps, affords the most 
 conspicuous instance of the morphologic distinction between the 
 
THE PINEAL BODY 231 
 
 end-vesicle and the proximal portion of the pineal organ. Were 
 it not for a slender fasciculus of nerve fibers these two portions 
 of the epiphyseal complex would appear as independent entities. 
 As it is, both parts are well differentiated and well developed, 
 one as an eye-like organ, the other with some of the characters 
 of a gland. This distinction between the end-vesicle and prox- 
 imal portion should not be underestimated. It not only shows 
 how remote the relationship between the two parts may be, 
 but also gives an added prominence to the proximal portion. 
 This latter part has already been shown to be the most constant 
 element in the epiphyseal complex, while the end-vesicle is much 
 more limited in its occurrence. 
 
 The process by means of which the end-vesicle and proximal 
 portion of the pineal organ are rendered so distinctive in amphibia 
 takes on a new phase in Sphenodon and lacertilia. In these 
 forms the necessity for the end-vesicle to assume visual char- 
 acters has apparently ceased, and this structure together with 
 the stalk is evidently in a state of involution. The contrary, 
 however, is true of the proximal portion which has taken on 
 not only more conspicuous dimensions, but also more pro- 
 nounced glandular characters. In the ophidians, in birds, and 
 in mammals the process of involution in the end- vesicle and 
 stalk has been carried to its final stage. No trace of the end- 
 vesicle or the stalk is to be found in any of the orders above 
 lacertilia. The proximal portion, on the other hand, in ophidi- 
 ans, birds, and mammals gains prominence because of its 
 glandular structure. 
 
 The process here described from amphibia to mammals clearly 
 demonstrates the progressive involution of the eye-like end- 
 vesicle and the gradual ascendency of the glandular proximal 
 portion. At one end, namely in amphibia, the end-vesicle and 
 proximal portion must be regarded as coordinate in prominence. 
 At the other end, i.e., in ophidia, the proximal portion is pre- 
 eminent because of the disappearance of the end-vesicle. This 
 phenomenon can best be interpreted on the basis of a pluri- 
 potentiality in the anlage of the epiphyseal complex, of such a 
 nature that the adaptive possibility for the development of a 
 
232 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 parietal eye or of a gland, or the simultaneous development of 
 both of these, is given in their origin. 
 
 According to this conception, it is not possible to consider the 
 parietal eye as primordial; it seems far more likely that it is an 
 adaptive modification developing in response to special require- 
 ments in a limited number of forms. The proximal portion, on 
 the other hand, maintains its entity with such marked per- 
 sistency throughout the series that it seems possessed of the more 
 primitive characters. This is emphasized when the proximal 
 portion is considered in connection with the other glandular 
 derivatives of the diencephalic roof. Embryologically, in those 
 instances in which both an eye-like end- vesicle and a glandular 
 proximal portion develop the anlage of these parts must have 
 been pluripotential. This is equally true in the instances in 
 which one portion of the epiphyseal complex, as, for example, the 
 parapineal organ, develops an eye-like structure while the 
 pineal organ develops a marked tendency to glandular formation. 
 Such an interpretation of the pluripotentiality in the epiphyseal 
 anlage when applied to the various orders reveals the following 
 conditions : 
 
 In cyclostomes the epiphyseal anlage seems to contain ele- 
 ments which are exclusively engaged in the differentiation of 
 eye-like structures which form the pineal and parapineal eyes. 
 
 In selachians, ganoids, teleosts, and dipnoians the epiphyseal 
 anlage has completely lost its potentiality to differentiate as a 
 visual organ, and while there may be some debate as to the 
 character of the adult structures, there is some evidence which 
 points to their glandular nature. 
 
 In amphibia both potentialities are present in the pineal 
 organ. In Sphenodon and lacertilia both potentialities are also 
 present, but in these instances the parapineal portion of the 
 epiphyseal complex gives rise to the eye-like structure while the 
 pineal portion develops glandular characters. In ophidians and 
 all the higher vertebrates the potentiality for the development 
 of visual structures is lost. 
 
 Even accepting the probability of this dual potentiality, it 
 should be borne in mind that the median eye-like structure may 
 
THE PINEAL BODY 233 
 
 in no instance signify a functionally active visual organ. In all 
 cases the attempt to develop a median eye may represent but 
 the abortive and partially attained differentiation of far remote 
 primitive ancestors in which such an eye was functionally active. 
 Its persistence into extant forms even as an abortive structure 
 may thus be taken to indicate the transmitted potentiality of 
 the epiphyseal complex to develop a visual organ. 
 
 The theory that the two elements in the epiphyseal complex, 
 namely, the pineal and parapineal organs, represent a pair of 
 parietal eyes similar to those of invertebrates, has little to recom- 
 mend it. The hypothesis of Dendy 86 that the ancestral verte- 
 brates were possessed of. such a pair of visual organs, while 
 interesting, is based upon too few facts in living vertebrates to 
 justify its acceptance. After considering the several theories 
 concerning the relation of the parietal eye to the pineal body, we 
 have come to the conclusion that none of them is adequate to 
 explain all of the facts. But with a full appreciation of the 
 investigation already devoted to this subject we desire to offer 
 a new interpretation which to us seems more tenable. Accord- 
 rag to our views, there is no direct relation between the parietal 
 eye and the pineal body, but each is of itself an adaptive modifi- 
 cation answering the demands for, or representing an inherent 
 impulse toward, the development of a parietal eye, on the one 
 hand, or of a glandular organ, on the other. In other words, the 
 epiphyseal anlage is pluripotential in its derivatives. 
 
 5. The phylogenetic significance of the parietal eye with reference 
 to vertebrates and invertebrates 
 
 Much has been written concerning the significance of the 
 parietal eye as one of the possible indices in the evolution from 
 invertebrates to vertebrates. Although little evidence bearing 
 upon this point has been presented in the general consideration 
 of this work, the subject seems of enough interest to warrant the 
 inclusion of the views of certain investigators who have devoted 
 some attention to this matter. 
 
234 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 Mathias Duval 98 in 1888 brought to a conclusion a notable 
 series of lectures with the statement that the history of the 
 pineal gland has played an important role in the study of homolo- 
 gies in the structure of the vertebrates and invertebrates. 
 He further states that the situation of the pineal body in rela- 
 tion to the nervous system of vertebrates and in comparison 
 with the oesophageal ring in invertebrates gives the structure 
 a new significance. From this it might be possible to determine 
 one of the clews which should reveal how the vertebrates resulted 
 from the successive transformation of the invertebrates. 
 
 Several years prior to this observation, Ahlborn 2 suggested 
 that the parietal organ was comparable to the unpaired eye of 
 amphioxus and tunicata, while Rabl-Ruckhard 322 was of the 
 opinion that an homology existed between the pinal organ and 
 the parietal eye of arthropoda. Baudouin 15 expressed the view 
 that of the proto-vertebrates, larval ascidians possess an un- 
 paired eye which, however, disappears in the adult. This organ 
 is situated immediately beneath the epidermis and consists of 
 a retina, a lens, and a pigment layer. It is derived from the 
 cerebral vesicle and supposed to be the vestige of a transitory 
 eye which previously existed in adult ascidians. Indeed, in 
 pyrosomes this unpaired eye is well developed in the adult, 
 possessing a retina, lens, and optic nerve.. There are no lateral 
 eyes in these invertebrates, and hence the unpaired eye must 
 functionate as a visual organ. In tunicates there exists both 
 the paired and unpaired eyes. In amphioxus there is a pig- 
 mentary patch placed above a dilation of the brain, but one 
 is not justified in considering this the homologue of the unpaired 
 eye in tunicates. 
 
 Peytoureau 3083 held the opinion that the pineal eye exists in 
 vertebrates in a degenerated state only. In extant forms of 
 the tunicates it still exists as a functional organ, occupying in 
 these animals almost exactly the same position and having the 
 same disposition as in lizards and amphibia. In tunicates there 
 is an unpaired eye and two paired eyes which he believes func- 
 tionate simultaneously, the unpaired eye being comparable to 
 the parietal eye of the lizard and amphibia not only because of 
 
THE PINEAL BODY 235 
 
 its position, but also because of its anatomy and connections. 
 He is of the opinion that the unpaired eye is more ancient than 
 the lateral eyes. This is the more probable since the ancestors 
 of the vertebrates were mon-ophthalmic, examples of which are 
 to be found in the pyrosomes which have but a single median 
 eye. Subsequently, the lateral eyes make their appearance in 
 tunicates and these functionate simultaneously with an unpaired 
 eye. Peytoureau 3083 gives six diagrams showing the degenera- 
 tive process from the median eye of pyrosomes to the epiphysis 
 in the higher mammals, as follows: 1, In pyrosomes, a simple 
 vesicle with a lens; 2, in larval urodela there is a vesicle with 
 nerve connections and nerve centers but no lens; 3, in chamaeleon 
 there is only an epithelial vesicle which has no connections or 
 neural characteristics; 4, in batrachians the organ is a detached 
 epithelial cluster having no connection with the central nervous 
 system; 5, in cyclodus the organ is a gland attached to the third 
 ventricle by means of a peduncle; 6, in mammals and birds it is 
 connected with the brain by a solid pedicle but presents no vesicle. 
 Gaskell, 146 in his summary concerning the evidence of the 
 organs of vision and their bearing upon the origin of vertebrates, 
 writes as follows: 
 
 The most important discovery of recent years which gives a direct 
 clue to the ancestry of the vertebrates is undoubtedly the discovery 
 that the pineal gland is all that remains of a pair of median eyes which 
 must have been functional in the immediate ancestor of the vertebrate, 
 seeing how perfect one of them still is in Ammoccetes. The vertebrate 
 ancestor, then, possessed two pairs of eyes, one pair situated laterally, 
 the other median. In striking confirmation of the origin of the verte- 
 brate from Palseostracans it is universally admitted that all the Euryp- 
 terids and such-like forms resembled Limulus in the possession of a 
 pair of median eyes, as well as a pair of lateral eyes. Moreover, the 
 ancient mailed fishes, the Ostracodermata, which are the earliest 
 fishes known, are all said to show the presence of a pair of median eyes 
 as well as of a pair of lateral eyes. This evidence directly suggests that 
 the structure of both the median and lateral vertebrate eyes ought to 
 be very similar to that of the median and lateral arthropod eyes. Such 
 is, indeed, found to be the case. 
 
 The retina of the simplest form of eye is formed from a group of 
 the superficial epidermal cells, and the rods or rhabdites are formed 
 from the cuticular covering of these cells; the optic nerve passes from 
 these cells to the deeper-lying brain. This kind of retina may be called 
 
236 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 a simple retina, and characterizes the eyes, both median and lateral, 
 of the scorpion group. 
 
 In other cases a portion of the optic ganglion remains at the sur- 
 face, when the brain sinks inwards, in close contiguity to the epidermal 
 sense-cells which form the retina; a tract of fibres connects this optic 
 ganglion with the under-lying brain, and is known as the optic nerve. 
 Such a retina may be called a compound retina and characterizes the 
 lateral eyes of both crustaceans and vertebrates. Also, owing to the 
 method of formation of the retina by invagination, the cuticular sur- 
 face of the retinal sense-cells, from which the rods are formed, may be 
 directed towards the source of light or away from it. In the first case 
 the retina may be called upright, in the second inverted. 
 
 The evidence of the optic apparatus of the vertebrate points most 
 remarkably to the derivation of the Vertebrata from the Palseostraca. 
 
 Gaskell, in this argument, seems to have lost sight of his 
 well-known contention that the roof of the brain in vertebrates 
 is to be considered the dorsal wall of the invertebrate stomach. 
 The Stress which he laid upon this relation, to which he gave 
 further emphasis by calling attention to the glandular appear- 
 ance of the roof-plate in Ammocoetes, does not coincide well 
 with his idea that the pineal body is primordially a portion of a 
 neural mechanism. He, of course, admits that the pineal eye in 
 vertebrates must be considered as resulting from a neural in- 
 vasion of the roof-plate, yet from his contention this roof-plate 
 is primitively the dorsal wall of the stomach, and neural deriva- 
 tives appearing in it must be due to a secondary neural invasion 
 and, therefore, cannot be considered primordial. 
 
 In a word, by holding the pineal eye to be fundamentally 
 neural in structure he did injury to his own theory concerning 
 the evolution of the vertebrates. 
 
 Patten, 303 in considering the significance of the parietal eye, 
 gives the following conclusions: 
 
 The parietal eye of vertebrates is homologous with the parietal eye 
 of such arthropods as Limulus, scorpion, spiders, phyllopods, cope- 
 pods, trilobites, and merostomes, but not with the frontal stemmata 
 or other ocelli of insects. 
 
 In the arthropods, various stages in the evolution of a cerebral eye 
 are shown in detail, from functional eyes on the outer margin of the 
 cephalic lobes, to a median group of ocelli enclosed within a tubular 
 outgrowth of the brain roof. 
 
THE PINEAL BODY 237 
 
 The most primitive type of a parietal eye is seen in the nauplii of 
 phyllopods and entomostraca, where the eye is a pear-shaped sac, open- 
 ing by a median pore or tube on the outer surface of the head. In the 
 higher arachnids, the process of forming an embryonic eye vesicle 
 merged with the process of forming a cerebral vesicle, the external 
 opening of the forebrain vesicle and that of the parietal eye tube, form- 
 ing a common opening or anterior neuropore. 
 
 The parietal eye of arthropods is an important visual organ until 
 the lateral eyes, which represent a later product, are fully developed. 
 It may then diminish in size and activity, but it rarely, if ever, wholly 
 disappears. 
 
 During the revolution of vertebrates from arachnids, there was a 
 considerable period during which the lateral eyes were adjusting them- 
 selves to their new position inside the brain chamber, and when they 
 were in functional abeyance. At this period, ancestral vertebrates 
 were mon-oculate, that is they were dependent solely on the parietal 
 eye, which had come to them from their arachnid ancestors as an 
 efficient and completely formed organ. 
 
 When the lateral eyes again became functional, the parietal eye 
 began to decrease in size and effectiveness. 
 
 The parietal eye is the only one now present in tunicates. In the 
 oldest ostracoderms, like Pteraspis, Cyathaspis, Palseaspis, the lateral 
 eyes are absent, or at least do not reach the surface of the head, the 
 only functional one being the parietal eye, which is of unusual size. 
 
 In the lampreys we see the same conditions, the parietal eye being 
 very well developed in the larvae, while the lateral eyes are deeply 
 buried in the tissues of the head, and useless. During the transfor- 
 mation, the lateral eyes again become functional, and the parietal 
 begins to atrophy, finally losing many of its structural details and its 
 function, although still retaining very nearly its original form. 
 
 All the theories advanced concerning the significance of the 
 parietal eye as an index to the process of evolution from the 
 invertebrates to the vertebrates have their great value in the 
 suggestions which they offer. To accept any of them without 
 further evidence seems unwise at the present time. It is pos- 
 sible to conceive of the median eye of invertebrates as analogous 
 to the parietal eye of vertebrates. It is, however, a long step 
 for the most part without the intervening support of evidence to 
 maintain that these structures are homologous. In fact it 
 seems out of the question to establish any such basis of compari- 
 son until this subject of homology in the invertebrate and verte- 
 brate brain is on much firmer ground than it is to-day. It is 
 evident that nothing short of the definite establishment of an 
 
238 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 invertebrate pineal region of the brain can satisfy the require- 
 ments in this field of homology. Not only must such an area in 
 its general outlines be recognized, but the demonstration must 
 be given that every element entering into it has its homologue 
 in the vertebrate brain. For this reason it seems impossible at 
 present to accept any other view than that the median eye in 
 invertebrates and the parietal eye of vertebrates are analogous. 
 The supposition that they are homologues, however suggestive 
 and stimulating, can hardly be regarded, at present, as other 
 than speculative morphology. 
 
 8. SUMMARY AND CONCLUSION 
 
 I. The pineal region is preponderatingly glandiferous in its 
 derivatives. The morphogenetic impulse imparted by such 
 a gland-forming area could not fail to have a profound influence 
 upon one of its constituents, the epiphysis. 
 
 II. a. The pineal body cannot be a vestige from the evidence 
 based upon its gross morphology, for the following reasons: , 
 
 1. The phyletic constancy of the epiphysis in the vertebrate 
 phylum. 
 
 2. Its variations and morphologic specializations. 
 
 3. Its relatively greater phyletic constancy with reference to 
 other structures in the pineal region. 
 
 4. The gross evidence of its progressive specialization in 
 ophidians, birds, and mammals. 
 
 5. The increase in the epiphy so-cerebral index, from the 
 earliest stages to the latest periods of life in man. 
 
 6. The resistance to the encroachment of a prominent neo- 
 morph in the mammalian brain, that is, the corpus callosum, 
 which has produced such marked alterations in the other con- 
 stituents of the diencephalic roof-plate. 
 
 b. The pineal gland cannot be considered a vestige in the 
 light of the histological evidence, since the tendency toward 
 specialization is definitely in the interest of glandular formation 
 in ophidians, chelonians, birds, and mammals. Ontogenetically, 
 in two forms at least, in Felis domestica and man, the develop- 
 
THE PINEAL BODY 239 
 
 ment of the pineal body follows the general lines of glandular 
 differentiation. The pineal body is, therefore, a glandular 
 structure and as such, is necessary in some way to metabolism. 
 
 III. The histology of the organ gives clear evidence that the 
 epiphyseal complex of vertebrates possesses a pluripotentiality 
 whose fundamental inherent tendency is in the interest of glandu- 
 lar differentiation, but in a few instances, as in cyclostomes,. 
 amphibia, and in primitive reptiles, the pineal organ may become 
 further differentiated in the interest of a highly specialized 
 sensory mechanism which has, or has had, visual function. As 
 a gland, it may in some cases, contribute its secretion to the 
 cerebrospinal fluid, but in the higher vertebrates, as in ophidians, 
 chelonians, birds, and mammals, it is an endocrinic organ, 
 contributing the products of its secretion to the blood stream. 
 
 IV. a. There is no direct relation between the parietal eye and 
 the pineal body, but each is of itself an adaptive modification 
 answering the demands for, or representing, an inherent impulse 
 toward the development of a parietal eye, on the one hand, or a 
 glandular organ, on the other. 
 
 6. The pineal body as it appears in mammals cannot be 
 regarded as the vestigial or metamorphosed degenerated or 
 atrophic residuum of the parietal eye in vertebrates. 
 
 V. The phylogenetic significance of the parietal eye in verte- 
 brates as the homologue of the median eye in invertebrates 
 should be accepted with much reservation. Until such time as 
 the homology between the vertebrate pineal region and some 
 corresponding area of the invertebrate brain is much more firmly 
 established than at present, the parietal eye as an index in the 
 evolution of the vertebrates from the invertebrates has but little 
 value. 
 
 The authors desire to acknowledge their great indebtedness 
 and to express their appreciation to Professor George S. Hunt- 
 ington for his assistance in the preparatine of this monograph. 
 They also wish to express their thanks to Professor M. Allen 
 Starr for his liberality in supplying the means which have made 
 publication possible. 
 
240 FREDERICK TILNEY AND LUTHER F. WARREN 
 
 
 
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242 FREDERICK TILNEY AND LUTHER F. WARREN 
 
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THE PINEAL BODY 243 
 
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244 FREDERICK TILNEY AND LUTHER F. WARREN 
 
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THE PINEAL BODY 245 
 
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THE PINEAL BODY 247 
 
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THE PINEAL BODY 249 
 
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THE PINEAL BODY 253 
 
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