,^,v^ THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID LESSONS ON SHELLS, AS GIVEN TO CHILDREN BETWEEN THE AGES OF EIGHT AND TEN, IN A PESTALOZZIAN SCHOOL, BY THE AUTHOR OF "LESSONS ON OBJECTS. ILLUSTRATED BY TEN PLATES, DRAWN FROM NATURE. SECOND EDITION. PUBLISHED BY R. B. SEELEY AND W. BURNS! DE : AND SOLD BY L. AND G. SEELEY, FLEET STREET, LONDON. MDCCCXXXVIII. -H0S o 6 PREFACE. Quin ipsis doctoribus hoc esse curae velim, ut teneras adhuc mentes more nutricum mollius alant, et satiari veluti quodam jucundioris disciplinae lacte patiantur. Erit illud plenius interim corpus, quod mox adulta setas adstringat. Hinc spes roboris. QUINTILIAN. ' LESSONS on Shells ' may be considered as a continuation of ' Lessons on Objects ; 9 the principles of teaching illustrated in that little work are here applied to an important and inter- esting branch of Natural History. It is, like its unpretending predecessor, a transcript of the actual labours of the class-room ; and friends who have visited the school, may retrace in the printed work the process of which they were witnesses. The end for which it is now laid before the public is not that it may serve as an instructive and entertaining volume to be placed in the hands of children; this end is sufficiently attained by several works of acknowledged merit ; which, in order that the subject may be more familiarly handled and more vividly con- ceived, represent an imaginary group of pupils vi PREFACE. conversing and receiving instruction. The ob- ject my sister has proposed to herself is to place a volume in the Teacher's hands which shall help him to re-act with his pupils the scenes that are here described. It is not a drama offered for perusal in the closet, but a manager's copy commended to the conductors of other theatres of education, to enable their liliputian corps dramatiques to assume the same characters, play the same parts, and I will not say, " fret their little hour upon the stage," but enjoy the genuine delight of intellectual activity judi- ciously directed. A want of order and arrangement in the early part of ' Lessons on Objects/ has been alleged as a blemish in that work ; but, in point of fact, its miscellaneous character was a studied feature, as better suited to the intellectual state of the pupils. Their first step should be the exami- nation of objects as nature presents them, or rather as they see them in nature, that is, either as insulated or as associated only by accidental connection. When ideas are formed and correct expressions familiarized, the business of classifi- cation commences, the lessons assume a more scientific character, and the pupils are prepared to enter on the province of Natural History. The training, then, which ' Lessons on Objects' will have supplied for commencing ' Lessons PREFACE. vii on Shells,' will consist principally in the im- proved faculty of observing natural features, in the possession and command of a small voca- bulary of scientific terms, in the habit of classification, and in tlie practice of giving a written summary of the knowledge acquired. Several circumstances concur to recommend conchology as the first branch of Natural History to be studied by younger pupils. Shells are of themselves interesting, from the peculiarity of their forms and the variety of their colours ; their characteristics are simple and present themselves readily to the eye, and a variety of interesting information may be given respecting the animals which inhabit them. Added to this the greater part of the specimens may be procured at little expence, may be easily preserved, and therefore continually re- produced to the class, and besides may, without fear of damage, be committed to the careless hands of the youngest students. It will however, I know, be objected by staunch anti-reformers in education, that im- prove the mode of teaching Natural History as you will, you but teach better that, which had better not be taught at all ; for that whatever abridges the time given to classical instruction, weakens the nerves and sinews of the mind, and but debases the Corinthian viii PREFACE. column of ancient lore by introducing the barbarous ornaments of modern science. My answer is, we do not propose to devote a large portion of time to Natural History in ordinary cases, and even this will be taken principally during those early years when very little real progress is made in Greek or Latin. Every age has its intellectual, as well as its moral claims ; and though the stern discipline of early classical instruction may offer some advantages, still the hours devoted to the abstractions of grammar, and the puzzling out ideas which have no pro- totype in the child's mind through the dark mist of a language little akin to his maternal tongue, present very meagre food to that under- standing they are supposed to strengthen. If the child must lisp in Latin, let him do so ; let his first Gradus ad Parnassum be through the quagmires at its base ; the few choice spirits that mount the summit may, perhaps, tread it with firmer step, and enjoy the prospect with keener relish ; but that step will riot be the less firm, nor that relish the less keen, because a daily hour was abstracted for ' Lessons on Ob- jects,' or ' Lessons on Shells.' Not only are the sciences so linked together that each gives each a double charm, but the faculties of the mind are so constituted, as that the vigour of each is promoted by the due developement of the rest. PREFACE. ix And there is a harmony as truly existing in a properly educated mind, as in a well- formed and well-exercised body, though the harmony of the former may not be so easily discerned as that of the latter. ;' As years advance, the study of Natural His- tory may be confined to those who manifest a peculiar taste for it, or who exhibit little dispo- sition for classical pursuits. For, as every age has its intellectual claims, so also has every grade of talent. The schools of the highest reputation have generally been conducted too exclusively to the advantage of the superior class of minds. The fine porcelain has been beautifully moulded and delicately pencilled, but the coarser clay has been almost entirely neglected. Yet many a young man who will never shine in the Senate House or the Schools, may yet pursue Natural History with success, and find in such pursuits improvement for his mind, a refuge from ennui, and a substitute for sensual pleasures. There is much truth as well as benevolence in a remark, I once heard from an amiable coadjutor of Pestalozzi ; " Tout terrain est bon si Ton sait le cultiver." Much of the instruction thus communicated, will doubtless fade from the mind ; but not with it will pass away all the benefits arising from these studies. In after years they may be recom- x PREFACE. menced with greater facility, in consequence of the early training ; and every incidental reference to these subjects, which conversation or litera- ture may present, will be more readily seized, and more clearly comprehended. And may it not be anticipated, that through the judicious introduction of these branches of education into our schools, the latent powers of genius may be kindled, and talents elicited that shall push forward the limits of science,* and force the Proteus nature to reveal still more of her secret truths ? C. MAYO. Cheam, June 15, 1832. * In confirmation of this idea it may be stated, that a very ingenious improvement of the dissecting microscope, which has merited a reward from the Society of Arts, has been invented by a very young person brought up on these principles. I have the more unmixed pleasure and honest pride in mention- ing this fact, as it refers not to a pupil of my own, but to one educated at Stanmore. PREFACE TO THE SECOND EDITION. IT has been objected to these Lessons, that the children are instructed in the system of Lin- naeus, one confessedly imperfect, instead of that of Lamarck, which has been drawn out since the science has been enriched by modern discoveries. This objection would be most reasonable if the chief aim proposed in the work had been to teach the science of conchology, but it is in fact simply what its name imports, LESSONS ON SHELLS ; having for its object, to develope children's powers of observation, comparison, and classification : and to cultivate habits and tastes, which may in after life lead to a more correct and scientific study of the subject. In- tellectual power and not knowledge, being the desideratum, that system should be pursued, which the children can work out ; and there can be no doubt that the Linnrean is the best adapted for this purpose. The genera of Lamarck are principally determined by the animal which the children could not, with the exception of a very xii PREFACE TO THE SECOND EDITION. few instances, have the opportunity of examining indeed many of the shells composing his genera are very rare, and they could only know them by pictures ; the generic distinctions also are often so minute that they would elude the observations of minds unpractised in scientific details. There is on the contrary something in the simplicity and clearness with which the great Swede seized and defined the broad outlines of nature peculiarly suited to the capacities of the young; and they may be led with very little assistance, to group the shells according to his arrangement, and to draw out from their own observation the generic characters. Nor will an acquaintance with the Linnsean system be with- out its value, when they may desire to study a more perfect classification than his; they will find the task of subdividing, separating, and arranging very much more easy than if they had to work upon materials altogether new to them ; they will have points established in their minds to which they may compare and attach the new ideas presented ; their perceptions will be quick- ened to discover similarities and differences ; and they will find many of the difficulties that em- barrass the student at the very threshold of science, overcome by their previous lessons. Some again have objected to the subject of the lessons, as being so much less interesting than PREFACE TO THE SECOND EDITION. xiii that of plants or animals. This, however, is a mistake; the well-defined, and varied forms of shells, their beautiful colours and markings, render them particularly attractive, and afford better opportunities than any other branch of natural history, for calling into action the per- ceptive powers. They are well suited to succeed " Lessons on Objects ; " the specimens may be examined in the same manner, and their parts and qualities described, and no other science present the same facilities of bringing before children, and exercising them in, the principles of classification. An additional interest is given to the study, when the accordance of the shell with the habits of its animal can be traced. In drawing out ' Lessons on Shells,' the fol- lowing works have been consulted, and extracts made from them. Burrows' Elements of Conchology.. Turton's Conchological Dictionary. Turton's Bivalve Shells of the British Isles. Mawe's Conchology. Montagu's Testacea Britannica. Flemming's Philosophy of Zoology. Lamark's Historic Naturelle des animaux sans Vertebres. The Conchologist's Companion. Shaw's Nature displayed. Sowerby's Genera of Recent and Fossil Shells. Dillwyn's Descriptive Catalogue of Recent Shells, The plates which illustrate this work, have been drawn from specimens actually presented to the class ; they are intended as an assistant to the teacher, but not as a substitute for the shells themselves in the instruction of pupils. LESSONS ON SHELLS. LESSON I. ON THE MOLLUSCA. Teacher. Do you know what these things are which I have brought in as the subject of our lesson to-day ? Child. They are shells. Teacher. Describe to me what you mean by a shell. Child. Oh, a shell is that which covers a snail. Teacher. Very true ; a snail has a shell, but in saying this you do not explain to me the na- ture of a shell. When you attempt to describe anything, you should give such an account as would instruct a person altogether ignorant on the subject. Try again, and tell me what a shell is. Child. A shell is a hard covering or house belonging to animals resembling slugs. B 2 LESSON I. Teacher. Of what use do you suppose shells to be? Child. They must be a defence and protec- tion to the animals which they cover. Teacher. Yes : shells are the hard coverings of certain animals called mollusca, or mollusks ; a name derived from mol Us, soft ; and esca,flesh ; if you call to mind the animals enclosed in these cases, you will not fail to observe how appli- cable this term is to them. Give me some exam- ple to prove that this name is well chosen. Child. The snail has a very soft fleshy body. Teacher. Yes, arid the mollusks in this res- pect are all alike. I have brought you some to examine; look at them well, and try and dis- cover the characteristics which distinguish them from other animals. Here are a snail, an oys- ter, a muscle, and a slug. Child. We shall not be able to say much about such animals as these, they are so shape- less and uninteresting in their appearance. Teacher. Do not form so hasty a judgment. T hope soon to convince you that it is your igno- rance alone which causes you to view them with indifference. There is not any part of the creation which you can study, that will not repay you for your labour ; and when you be- come better acquainted with the different king- doms of nature, you will experience an increased pleasure in your walks; and objects that you have hitherto passed heedlessly by, will rivet your attention by the wonders they unfold to you ; MOLLUSCA. 3 above all, my desire is that you should be led to trace in all that nature presents, the hand of an Almighty and beneficent Creator. When you are struck with the organization of a plant, fitting it for some particular purpose, or see the means of defence possessed by one animal, of attack by another, should your admiration rest in these instruments, whilst you forget Him who prepared and fitted the instrument for its appointed work ? Suppose that you have yourself made or done anything very nicely and with great pains for a friend, would you feel satisfied, or think it just, if, whilst your performance was admired, you were forgotten ? Child. I should consider such conduct very unjust. Teacher. And what lesson do you suppose that I wish to teach you by drawing your atten- tion to your own feelings when your industry and ingenuity have been thus overlooked ? Child. That when we are strnck with the beauty and utility of any of God's works, we should praise him for his wisdom, and thank him for his goodness. Teacher. It is with such feelings that I wish you to study Natural History, and it would then prove a very delightful and profitable employ- ment.* You must now return to the consider- ation of the animals before you. Examine them * It is most important in giving instruction in Natural History, early to accustom children to recognise the God of nature in his works. If God be robbed of his glory, how B 2 4 LESSON I. carefully exercise your different senses upon them mark the various parts of their bodies consider to what use each part is likely to be destined and reflect upon what you know of their habits. By using well your senses and your judgment, you will be able to find out much for yourselves. When you are at the sea-side, or out at sea, you may collect facts illustrative of the history of these animals. Child. That would be exceedingly interesting, Teacher. Yes it would ; but you need not wait for such "opportunities. Rivers, and even the garden, will afford you specimens for obser- vation : but what have you now to do ? Child. To examine the animals before us, to use our senses upon them as we did in our lessons on objects, to name their parts, and the uses of their parts as far as we know them. Teacher. Yes. I wish you first to observe these creatures attentively ; and that you may discover readily what is peculiar to them, you must in your own minds compare their qualities, can we anticipate a blessing on our labours ? Has not expe- rience proved, that the study of the wonders of creative wisdom does not lead the natural heart to the Creator ? Is it not notorious, that amongst the followers of science is con- tinually seen the practical, if not the avowed Atheist. Let this be a beacon to the Christian instructor, and let it be his careful endeavour to guard against the fatal error of speaking of God's works independently of him. As we are called upon to walk by faith, and not by sight, it is essential to lead chil- dren to see God in all things, and to trace Him who is him- self invisible in those outward manifestations of his power and goodness, which are within the reach of their observation. MOLLUSCA. 5 parts and habits, with what you know of other animals. First, tell me some qualities that appear to you to be common to all the mollusca. Child. Their bodies are soft, fleshy, moist, and cold. Teacher. Yes, you remember their name is given to them from their softness. Observe also the action of a snail when you come near to it. Child. It draws its body into its shell for protection. Teacher. Yes. The bodies of the Mollusca are contractile, that is, have a strong power of con- traction which they exercise by means of muscles. What more do you remark in these creatures ? Child. They have a thick skin which appears loose in some of them. Teacher. This skin is called the sac or man- tle ; and is peculiar to the molluscous tribe. It is constantly moistened by aslimy exudation, and is also full of pores and glands, of which I shall have occasion to speak in a future lesson. What are pores ? Child. Pores are very small holes. Teacher. What do you know about glands ? Child. I do not exactly know what glands are ; but we have glands in our throats, are those of the mollusks the same as ours ? Teacher. They are of the same nature, but much smaller than those in our throats. The office of glands is to secrete or separate fluids of various kinds from the general fluid of the sub- 6 LESSON I. stance. Animals as well as vegetables, are supplied with a greater number of glands ; the tears of animals are an example of secretion formed by means of such organs, so is the honey of plants. As the glands form little reservoirs, they often appear like small swellings, percep- tible to the sight and touch. Now can you tell me what glands are ? Child. They are organs by which are secre- ted some particular fluid from the general fluid of the body. Teacher. To return to the mantle ; it some- times envelops the mollusk like a purse, leaving an opening only where its mouth is situated ; sometimes it extends on the two sides, forming expansions which perform the part of fins. Sometimes it spreads over the shell itself, which in this case has always a fine polish. Compare, as I desired you, the mollusk s, with other animals, and tell me what further peculiarity you discover in them. Child. They have no bones, their bodies are only a mass of soft flesh. Teacher. They have certainly no bones ; but in the mollusks which we purpose studying, the shell, by acting as a support to the body, seems in some measure to answer the purpose of bones. What more do any of you discover in these animals ? Child. They do not appear to have any blood . Teacher. They have not red blood as we have ; but are they composed entirely of solid matter ? MOLLUSCA. 7 Child. No, for when a snail is trodden upon, a white fluid issues from it ; is this its blood ? Teacher. Yes, it may be considered as a kind of blood. How does it differ from that which circulates through our bodies ? Child. It is white and cold. Teacher. True ; and in consequence some naturalists have not considered it as blood, and have described the mollusca to be exsanguin- eous ; a term signifying without blood, and derived from Latin ex 9 out of, and sanguine, blood. As this fluid flows through their bodie.s in vessels issuing from their hearts, it is now generally called their blood. What are you watching in the snail ? Child. The very quick manner in which it draws in its horns, and shrinks into its shell, if it is touched. Teacher. What would you determine with respect to the animal from this circumstance ? Child. That it has the sense of feeling. Teacher. Yes ; and which part appears most sensitive ? Child. The horns. Teacher. And do you observe how the little animal feels about, and tries with these projec- tions which you call horns ? They have from thence been termed Tentacula 9 from the Latin, tentare, to try or feel. How many tentacula have snails ? Child. Four. Teacher. The tentacuia vary in number ; 8 LESSON I. many mollusks have only two. The sense of feeling resides in the nerves. Child. Oh ! then the mollusks must have nerves. Teacher. Yes, they have nerves. Do you perceive any other organs of the senses besides the tentacula? Child. There are black specks on the horns of the snail which appear like eyes. Teacher. These specks are the organs of sight, of which mollusks have never more than one pair. The sense of seeing, however, is not universally possessed by this class of animals. The organs of hearing and smelling have never been discovered in any of them, but they are sup- posed to possess the latter from the readiness with which they select suitable food. This cir- cumstance also proves that they possess the sense of taste. You must now recapitulate all that has been said concerning the mollusca. Whence is the name derived ? Child. From mollis, the Latin for soft. Teacher. What kind of body have they ? Child. Cold, slimy, soft, and fleshy. Teacher. Yes ; and another quality you observed when I touched the snail several times. Child. That its body is contractile. Teacher. And what enabled it so quickly to contract its body, and retreat into its shelter ? Child. Its being furnished with muscles. Teacher. When you compare these animals MOLLUSCA. 9 with others, in what respect do they appear deficient ? Child. They have no bones, the shell acting as a support to their bodies, which are attached to it by muscles. Teacher. What envelops the mollusca ? Child. A sac or mantle. Teacher. Describe the mantle. Child. The mantle is full of pores and glands and is moistened by a slimy exudation some- times it quite encloses the animal, having only one opening like a purse, sometimes it has ex- pansions at the sides, like fins, and sometimes it spreads over the shell. Teacher. What are glands ? Child. Small lumps containing fluids, which are separated from the blood. Teacher. Yes, in animals the glands secrete fluids from the blood ; but in vegetables from the sap. Have these animals any blood ? Child. Yes ; but it is white and cold. Teacher. In what respects is it similar to blood ? Child. It circulates through the body in vessels issuing from the heart. Teacher. What senses are enjoyed by the mollusca ? Child. The senses of feeling, seeing, tasting, and, it is supposed smelling. Teacher. In what part of their frames is the sense of feeling most acute ? Child. In the tentacula. Teacher. Tell me the derivation of that term ? 10 LESSON I. Child. It is derived from the Latin, Tentare, to try. Teacher. But what must they possess in order to be able to feel ? Child. Nerves. Teacher. I will now read to you a summary of your lesson, and I shall expect you afterwards to write it from recollection. Teacher. The mollsuca have soft, slimy, cold, fleshy, and contractile bodies. They have no bones, but their shell acts as a support to their frame. They have muscles by which they are attached to their shells, and by which they move their bodies. They are enclosed in a skin called the mantle, or sac, which is full of pores and glands. Sometimes the animal is so completely enveloped in this, as only to present an opening where the mouth is situated, some- times it spreads over the shell, and sometimes it has external expansions answering the purpose of fins. The mollusca have not warm red blood, but a white cold fluid issues from their hearts and circulates through their frames. They have nerves, and consequently, feeling ; and this sense seems most accute in their tentacula. Some have eyes, but others do not enjoy the sense of sight. They appear to have the power of smel- ling and tasting, but no traces of ears have been discovered.* * This little summary of the substance of the lesson may be read over twice to the children, and they should then be MOLLUSCA. 11 LESSON II. ( To commence with a repetition of the summary of the former lesson.) Teacher. Examine these animals again, com- pare them with insects, and tell me if you observe any deficiency in their construction. Child. They have not any limbs. Teacher. Very true. They have not limbs or joints, as insects, nor are they divided, or moved by means of rings, as worms. Child. Yet they move about. Teacher. Yes ; the greater number of mollusks have the power of locomotion, that is, of moving from place to place ; the term is de- rived from the Latin locus, a place. We will required to write it as well as they can from recollection. It would be desirable also that they should repeat it at the com- mencement of the succeeding lesson. This process may appear tedious, but the result will be most satisfactory both to the teacher and pupils. The latter should acquire so clear a know- ledge of the facts brought before them, and have them so well imprinted on their minds, that they may, through all their progress, be enabled without confusion or hesitation, to recur to each preceding step. Their information should be like a chain, which is held unbroken in the grasp ; and when this is accomplished, a power of mind is elicited which,, independently of the knowledge obtained, will prove most valuable when applied to more important subjects. 12 LESSON II. first examine the organs by means of which this power is exercised. In what manner do snails and slugs make their way along the ground ? Child. Their skin expands at the sides of the body, and adheres to the earth, and then they draw themselves on. Teacher. This fleshy expansion under their bodies is full of muscles, which they dilate and contract at pleasure. It adheres like a sucker, and the animal advances by fixing the fore part to the ground and drawing the remainder after it. This instrument is called a foot. In some species, as the snail, it is attached to the under part of the body by its whole length, but in others it is free at one end, and can be extended or drawn in at pleasure. When it is free it is called a leg, and is generally tongue-shaped ; it is frequently used as an organ of motion, but sometimes the animal employs it as a paw for digging holes in the sand or mud. But do you think that this organ will enable the mollusks to advance in all the situations in which they are placed ? Child. No, not when they are in the water ; then they must swim. Teacher. Yes, and this action is performed either by the serpentine movements of the foot and body, or by the movement of expanded portions of the skin or tentacula, which forces them onwards in the same manner as oars pro- pel a boat. Child. Have all the mollusks that live in MOLLUSCA. 13 the water either tentacula or expansions of the skin? Teacher. No ; some have no such elongated parts. I think you might have discovered this yourselves by observing one of the animals before you. Child. Oh yes, the oyster. Such mollusks cannot move then. Teacher. That is not true of all, some are immoveably attached to the spot where they first received life ; but others have the power of leaping or shifting their positions with a sudden jerk, produced by rapidly shutting the two pieces of their shells ; others again transport themselves from one spot to another by the force with which they draw in and eject the fluid in which they live. Many species are furnished with a kind of bladder by inflating or contract- ing which they can rise or sink in the water as circumstances require. Try and enumerate the various means of locomotion possessed by the mollusca. Child. Many creep by means of a fleshy elongation, which is in some a foot, in others a leg. In the water they swim, making their way either by the serpentine movement of their bodies, or by the use of tentacula. Some can rise and sink in the sea, and some make a leap by rapidly closing their shells, or by drawing in water and suddenly forcing it out again. Teacher. When we study the different kinds of mollusca, I shall speak to you more fully of 14 LESSON IL their peculiar habits. Did you ever observe when you have been on the sea-coast, numerous shells clustered together on the rocks and stones ? Child. Yes, barnacles ; are they the animals which never move from the spot to which they are attached ? Teacher. Yes, the barnacles and many other mollusks live and die on the spot where their existence first commenced. Child. How are they fixed to the spot ? Teacher. Some of them, as the barnacles, are cemented to the rocks by the same sub- stance of which their shells are formed ; others have a less permanent mode of adhesion, and fasten themselves by means of a viscid liquid which they discharge from glands in their bodies ; some produce silky filaments, one extremity of which remains in connexion with themselves, while the other is fixed to marine substances, and thus anchoring themselves, they float secure in the ocean. The bundle of filaments which the animal draws from his body for this purpose is called a byssus.* Do you know any other shells that are with difficulty removed from the rocks ? Child. Yes, the limpet. Teacher. The manner in which this mollusk * The children should see and examine for themselves these contrivances. A pinna with its byssus, and barnacles on a stone are easily procured. The web of the spider would give them a good idea of the work of the pinna, being produced in a very similar manner. MOLLUSCA. 15 fixes itself upon the rocks, is very simple, though very curious. It forms within its shell, a vacuum, that is, a space free from air, derived from Latin, vacuws, empty. By filling up the hollow of the shell with the fleshy substance of its body, it expels the air, and having fastened its body to the rock by a viscid substance, con- tracts itself in the centre, thus leaving a space within the shell entirely free from air. As there then is no internal expansion of this fluid, the pressure of the external atmosphere meets with no resistance, and in consequence acts with so much force upon the shell, that it cannot be removed from its situation without great effort. Repeat to me now the different means of attach- ment used by the mollusca. Child. Some fix themselves by silky fila- ments called a byssus, some by a viscid cement, others by forming a vacuum, and others attach themselves to the rocks by the same substance of which their shells are made. Teacher. The shells which by any of these means are rendered stationary, are called fixed shells, the others free shells. Does anything strike you with regard to these two kinds of mollusca ? Child. The inhabitants of the fixed shells must be badly off. They cannot procure nour- ishment. Teacher. They cannot indeed go in search of it, but the continued motion of the waves, or the flowing of the tide brings a fresh supply of 16 LESSON II. water swarming with the little animals upon which they subsist, and some increase the rapi- dity of this supply, by forming currents in the sea. Child. What very clever contrivers these animals seem to be. Teacher. Yes, and your remark leads me to an important consideration, to which I wish to direct your attention. How do these little ani- mals know that it is well for them to attach themselves to other substances. How have they learnt to form the vacuum, or weave the silken filaments ? Child. Is it riot instinct that directs them 1 Teacher. Yes, but can you tell me what instinct is ? Child. It is something that guides animals. Teacher. Is man taught in the same way ? Child. No, we have reason, and can think about what we do. Teacher. Well, let us consider a little the difference between that which directs man, and that which guides other animals. Suppose a child were to see a fire for the first time : not knowing its nature, he might perhaps put his finger into it. Would he do so, do you think, a second time ? Child. No, he would recollect the conse- quences of having done so before. Teacher He would have learnt then from his own experience : but is all knowledge obtained by our own experience ; do you not know any thing but what you have discovered yourself ? MOLLUSCA. 17 Child, We learn from the accounts of others. Teacher. True, we are instructed by the experience of others. But watch any animal, a bee for instance : when it makes its cell, does it try several times before he succeeds ? Child. No, he does it perfectly at the first attempt. Teacher. Has it been taught by its own species ? Child. No. Teacher. What then is the difference between the principle that guides the bee, and that which guides man ? Child. Man is taught both by his own ex- perience, and that of others ; but the bee acts rightly without either. Teacher. Yes ; it is directed immediately by a principle implanted in it by the Creator. This principle is called instinct, and is well defined to be prior to experience, and indepen- dant of instruction. I will now read to you the summary of to-day's lesson attend, that you may be able to write an account of it from recollection. Many of the mollusca, though destitute of jointed limbs, have organs of motion ; some have a fleshy expansion extending the length of the body, called a foot ; this is full of muscles, by which it is moved, it acts like a sucker, and the animal advances by fixing the fore part to 18 LESSON II. the ground, and drawing the remainder after it. This organ is sometimes free, and can be ex- tended or contracted at pleasure ; it is then called a leg, and is used either as an organ of motion, or as a paw for digging holes in the sand or mud. In the water, some mollusca advance by means of the serpentine motion of their bodies, others by the movement of either expanded portion of the skin or tentacula. Some, quite destitute of any separate organs of motion, effect a change in their position by ingenious contrivances ; thus, the common scal- lops, by rapidly shutting the two pieces of their shell, can transport themselves a short distance ; and others send themselves forward by drawing in water and ejecting it again with great force. Many species are furnished with a kind of air bladder, by inflating or contracting which, they rise and sink in the water as cir- cumstances may require. Some, however, have no power at all of moving, but remain fixed through life to the spot where they commenced their existence. Their modes of attachment vary ; some firmly fix themselves by the same materials of which they make their shells : others glue themselves by a viscid cement drawn from glands in their bodies ; and, others throw out a byssus, and anchor themselves securely to some rock. The limpet, by forming a vacuum in his shell maintains a firm hold of marine sub- stances. The shells thus rendered stationary, are called fixed shells, whilst those inhabited by animals that move about, are termed free shells. MOLLUSCA. 19 LESSON III. Teacher. What organs in the mollusca have we considered ? Child. The organs of sense and of motion. Teacher, And what other organs are essential to animal existence ? Child. All animals must have organs by which they feed themselves. Teacher. Have you ever observed snails eating ? Child. Yes ; I have seen them devour a leaf, and I should think they must have teeth. Teacher. They have two jaws which are fur- nished with small teeth, fitted for cutting vege- table substances. Child. Have all the mollusca mouths like that of the snail ? Teacher. No, the mouths of the different species, as well as their other organs, are adapted to the peculiar wants and habits of the animals. Some have only a simple opening to receive the little animalcula brought to them by the waves, and which do not require mastication.* Most of those which live upon the produce of the vege- table kingdom have a muzzle with jaws which are either horny or armed with teeth, f The * The Oyster. t The snail. C 2 20 LESSON III. carnivorous * mollusca have usually a kind of proboscis ; this instrument is a fleshy pliable tube terminated by a round aperture, with a cartilagi- nous edge armed with little teeth. f The proboscis is supplied with muscles, by means of which the animal can protrude or draw it in at pleasure; many use it to pierce other shells, that they may suck out the flesh of the inhabitant. I have mentioned to you three different kinds of mouths which mollusks are found to possess ; describe them to me. Child. Some have only a simple opening, others have jaws, either of a horny substance, or armed with teeth ; and others possess a plia- ble fleshy proboscis, moved by muscles, and ter- minated by a cartilaginous ring which has teeth. Teacher. Which are the feeders upon vege- tables, and which upon animals,? Child. The mollusks which have a muzzle feed upon vegetables, those with a proboscis are carnivorous. Teacher. In feeding there is another point to be considered, how the food is to be brought to the mouth. How do we manage this operation ? Child. By means of our hands ? Teacher. And what makes it particularly needful that man should possess hands ? Child. His erect position. Teacher. You have often had an opportunity of watching some of the mollusks which are * From the Latin carne, flesh, and voro, I eat. t Voluta tnusica. MOLLUSCA. 21 vegetable feeders, you can tell me how they manage. Child. The snail feeds upon vegetables, it crawls upon its fleshy foot till it reaches a plant, and then gnaws it with its jaws. Teacher. The animal feeders stretch out their proboscis and catch hold of their prey, and some grasp it with their tentacula, and thus bring it within reach of their mouths. Those mollusks which have only an opening, have a supply of food brought to them by the continued movement of the waves and the flowing of the tides, and you must remember my telling you of some who ingeniously increase this supply by creating an eddy in the water. I have brought you an oyster and a snail, and wish you to com- pare them together, and tell me what appears to you to be the most striking difference between the two. Child. The snail has a head, but the oyster is only as oft lump of flesh, and has no appear- ance of a head. Teacher. Many of the mollusks like the oyster, have no obviously distinct head. This circumstance has led naturalists to divide these animals into two great classes. How should you think they are distinguished ? Child. One class contains those mollusks which have heads ; the other, those which are destitute of heads. Teacher. The former are called mollusca cephala from the Greek /ce^aXj (kephale) a head; the latter, mollusca acephala from the Greek 22 LESSON III. a without, and K