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Meps, piatea, charts, etc., mey be filmed at different reduction ratioa. Thoae too lerge to be entirely included in one expoaure are filmed beginning in the upper left hand comer, left to right and top to bottom, aa many framee aa required. The following diegrems illustrate the method: Lee cartee, plenchea, tableaux, etc., peuvent *tre filmAe i dee taux da rMuction diff Arents. Lorsque le document est trop grand pour Atra raproduit en un seul clichA, il est film* A partir de i'angle sup4rieur gauche, de geuche i droite. et de haut an baa, an prenent le nombre d'imegea nAcasseire. Les diegrammea suivanta illuatrent la mAthode. 1 2 3 1 2 3 4 5 6 1 8 86.] Is Littorina litorea Introduced or Indigenous f 931 a. (American Naturalist Extra, Nbvetnbcr, 1886.) IS LITTORINA LITOREA INTRODUCED OR INDIG- GENOUS? BY W. F. GANONG. IT is now nearly thirty years since Littorina litorea (Linn.), the English periwinkle, was first reported from American waters, but the question as to whether it has been recently introduced or was an original inhabitant of our shores is still unsettled. This mollusk, though not known by naturalists to occur upon the coast of Acadia and New England previous to its discovery at Halifax in 1857 by John Willis, is at present very abundant from the Gulf of St. Lawrence to Connecticut. Professor Verrill (Amer. Jour. Sci., iii, iv, p. 133, 1874) says of it • *' It has been supposed by several writers that this shell {L. litorea) has been recently and accidentally introduced from Eu- rope; but Dr. Dawson informs me that he collected it more than thirty years ago in the Gulf of St. Lawrence. It is abundant at Halifax, and we have other specimens from Kennebunkport, Me., Hampton Beach, N. H., and Provincetown, Mass. There is really no sufficient evidence that it was not an inhabitant of our shores before the advent of Europeans, but local in its habitats. It may have become more diffused in recent times by commerce, or it may have been overlooked formerly by collectors." The causes determining the geographical distribution of ani- mal and plant life arc a subject of the greatest importance to nat- uralists, and any contribution to it has its value. So peculiar s^nd mf 933 Is Littorina litorea Introduced or Indigenous ? [November, interesting are the known facts in regard to the distribution and spread in America of the shell we are considering, that an in- quiry into the nature of these facts, and a search for an explana- tion for them becomes a matter of more than special importance. The value of the settlement of the question as to whether Litto- rina litorea has been introduced in recent times or is a native of America, is not limited to the settlement of this fact only. It has a broader value as well, inasmuch as it has a bearing upon the science of the distribution of animals. It must be remembered that no species of animal or plant can, in the strict sense of the word, be indigenous to both Europe and America. If such were the case it would be necessary to sup- pose that the two independent lines of descent, either from a common near or remote ancestor, culminating in the species, had followed precisely identical courses of development. The latter would require precisely identical conditions of environment — and such we know would not exist upon two separate continents. Hence a shell which is common to two continents must in some way have been introduced from one to another. It may be intro- duced by the agency of man, or by purely natural and physical causes, such as ocean currents, etc. For want of a better term the word indigenous has been used in the present paper to apply to a species introduced in past time by natural agencies and now thoroughly established as a resident. Such a species is our so-called " native periwinkle," Littorina pailiata (Say). It is common to Europe, Greenland and America, and has existed for a long time in all three countries, being found fossil in the Post-pliocene of all of them. It will be presently shown that this shell was probably introduced from the continent in which it originated to the other by way of Greenland and Ice- land, and by strictly natural agencies. We therefore speak of it as indigenous to America, though whether its descent from its parent species took place here or in Europe we are unable to say. But we hope to be able to show that Littorina litorea did not exist in America until introduced from Europe by man, and that since the beginning o( the present century. Mr. John Wi lis, who was the first to announce its discovery in America (Trp.ns. Nova Scotia Inst. Nat. Sci., Vol. i), found it at Halifax in 1857. He considered it. to be indigenous to Nova Scotia chiefly for the reason that " some of the oldest inhabitants 1 886.] Is Littorina Utorea Introduced or Indigenous ? 933 have assured me that they have ' often picked the periwinkle, the same as the English one,' on the shores contiguous to Halifax when they were only school-boys." The only other evidence that has been found to show that the shell was known in Nova Scotia, previous to 1857, comes in a private letter to the writer from Mr. E. Gilpin, of Halifa::. He says : " Historical evidence in the shape of old English settlers shows it to have been known in the province as far back as 1800." How much reliance can be placed upon the unscientific evi- dence of old settlers is a question ; but granting that they did not confound it with the native form, and that they actually saw it previous to 1857, nothing more is proved than that the shell existed in Nova Scotia some years before Willis found it. Simi- larly it may be said of the fact that Dr. Dawson " collected it more than thirty years ago in the Gulf of St. Lawrence," that it proves (if granted) only that the shell was to be found there ear- lier than any published record shows. Or it may be that, if intro- duced, it was introduced at more than one point. It is somewhat remarkable, however, that, as will be shown farther on, no other collector found this conspicuous shell in the gulf until after 1870, although Dr. Dawson must have found it at least as early as 1844. We know that it increases with great rapidity wherever introduced. Why then, if it existed there, did it not increase sufficiently to enable some other collector to find it ? None of the lists of Bell, Whiteaves or Dr. Dawson him- self mention it until after 1870. It is to be regretted that we have not some record of Dr. Dawson's discovery of the shell so far back, besides the note by Professor Verrill who doubtless writes from memcry. If this shell be indigenous to our shores, it must have been confined, previous to say 1850, exclusively to the Nova Scotia coast. That this must be so is shown as well by other facts as by the many lists we have of New England and Gulf of St. Law- rence shells, all of which mention the native periwinkles, L. pal- liata, L. rudis} L. tenebrosa} while L. litorea never appears. That the latter could have been present but "overlooked by collectors " is altogether out of the question. It is a much larger and more conspicuous shell than the native forms, has the same habitats, and wherever it occurs at all occurs abundantly. ' For convenience we will consiiler these two to be distinct si^ecies, although they are probably varieties of the same species. 934 ^s Littorina litorea Introduced or Indigenous ? [November, Among the many lists of Nev/ England shells which might be named, the following have been selected : Gould's " Invertebrata cf Mass.," ist ed. (1841), mentions Z. palliata, rudis and tenebrosa but not litorea. Mighel's list of the shells of Maine* (1843) mentions I.. palliata, rudis and tene- brosa as occurring " in the greatest pri:»fusion," but L. litorea is not in the list. Reed's " Catalogue of the Shells of Mass."* (1845) mentions the same three but not litorea. Russell's " Retrospect of some of the Shells found in Essex county, Mass."' (1851), mentions the same three but not litorta. 'Tuft's "List of Shells collected at Swampsicolt «.ynn and vicinity" (1853") mentions the same three as abundant, but not litorea. Stimpson's " List of the marine Invertebrates of Grand Manan" (1854) mentions L.palltcta (= Z. littoralis) and Z. ntdis, but not Z. litorea. Tuft's " Catalogue of Shells in the State cabinet [of Mass.]" (1859) mentions the sam«! three but not litorea. Nor has it been reported until quite recently from the Gulf of St. Lawrence. Dr. Dawson's " A week in Gasp6"* (1858) mentions Z. rudis and L. palliata, but not Z. litorea. If Dr. Dawson found it in the Gulf of Lawrence " thirty years ago," it must have been at some other point. Robert Bell's " List of the Mollusca of Eastern Canada"* (1859) mentions L. pal- liata only. J. F. Whiteaves' •' On the marine Mollusca of Eastern Canada"' (1869) mentions Z. palliata {littoralis), L. rudis and Z. tenebrosa, but not Z. litorea. Although the evidence of these lists is only negative, their combined force is so strong (even had we no other evidence) that they practically prove that the shell did not exist upon the New England coast, and probably not in the Gulf of St. Lawrence, previous to the middle of the present century. Since 185/ its spread has been phenomenally rapid. A paper, by A. F. Gray, in Science News for 1879, gives many localities which it had come to inhabit upon the New England coast, and the known facts of its spread are thus summarized by Professor Verrill :^ " It is well known to American conchologists that this com- mon European species has become well established upon the New England coast within ten oi' twelve years, appearing first upon ' Boston Jour. Nat. Hist., IV. ' See for this as well as other lists, Binney's " Bibliography of American Conchol- ogy," Smithsonian, Vol. I. 'Jour. Essex county Nat. Hist. Soc, i. ■•Can. Nat., ill, 321. "Can. Nat., iv, 197. "Can. Nat., ii, IV. 48. See also Can. Nat., ii, iv, 270. 'Am. Jour. Sci., iii, xx, 251. V 1 886.] Is Littorina litotea Introduced or Indigenous ? 935 in Conchol- the coast of Maine about 1868 ; Dr. Dawson, however, states that he collected it on the shores of Nova Scotia at a much earlier date. I wish at present merely to put on record some additional data as to its recent progress along the coast. In 1873 it was collected in abundance at Saco, Maine, by the U. S. Fish Com- mission, and was found sparingly at Peake's island, Casco bay. In 1872 it was very rare at Provincetown, Mass., but in 1875 it was common there. In 1875 it was collected by the writer at Barnstable, Mass., on the shores of Cape Cod bay, in large quan- tities. In 1879 it had become exceedingly abundant at Province- town. In 1875 our parties found two specimens only on the southern shores of Cape Cod, at Wood's HoU, but in 1876 it was found to be common there, and is now very abundant. The first specimen found so far westward as New Haven was obtained by Professor S. I. Smith during the past winter ['79~8o]' Other sol- itary specimens have since been obtained here by E. A. Andrews and by J. H. Emerton. It is at present exceedingly abundant at Newport, R. I." It is spreading into the Gulf of St. I-awrence, too, finding prob- ably a congenial habitat in the warmer water of Northumberland straits, which contain so many southern forms. J. F. Whiteaves found it at Souris and Charlottetown, P. E. I., in 1873.^ Do not these facts afford an exceedingly strong argument that the shell has been introduced? Its rapid inciease southward shows that a favorable habitat was there waiting for it — a much more favorable one than the Nova Scotia coast. The conditions which determine its spread "were here at work a century ago, but it was not found anywhere in New England. As has already been pointed out, no species of animal or plant can be truly indigenous to the two continents. It must either have originated in one and spread to the other, or it must have originated at some other ^^oint and spread to both. A shell such as we are considering, which is at present common to both con- tinents must either have been introduced from one to the other by man's agency, or by purely natural means. If it can be shown that the natural means did not operate in this case, it would prove that man must have introduced it ; and the stronger the proba- bility of the former, the stronger will be that of the latter. Winds or the agency of birds, so active in the distribution of plants, could hardly operate upon a shell or its young. Ocean currents seem to be the only method of conveyance. But by no means could either L. litorea or L. palliatci directly cross the At- • Report on deep-sea dredging operations in the Gulf of St. Lawrence. 7!^ mm 936 Is Littofina litorea Introduced or Indigenous ? [November, lantic in such a way — they must have come, if they came by nat- ural means at all, by way of Iceland, Greenland and Labrador. This we find actually was the case with L. palliata. Where it originated the writer does not know, nor does it matter in the present connection, but certain it is that it is now common to England,^ Greenland,^ Labrador,' Acadia and New England. And not only does it exist in these places now, but it has for a long time past, for it is found fossil in Post-pliocene deposits- in England, in Southern Greenland" (Z. gr'dnlandica = L. palliata) and in Canada, though not actually in Acadia. Dawson reports it from the Post-pliocene of Gaspe,* and Lyell from Beauport.® We may hence conclude that L. palliata is, in the sense in which we have used the word, indigenous to America. But as to L. litorea, not only does the latest and best list of Greenland shells^ make no mention of its occurrence there, nor does Packard in a list of the shells of Labrador' (though he men- tions L. palliata and L. rudis as " abundant " and " not uncom- mon "), but no trace of it has as yet been reported from any Post- pliocene deposits of Greenland, Labrador, Canada or New Eng- land. It is a shell much more likely to be preserved in such de- posits than L. palliata, being much larger and stouter — though neither, from their rock-loving nature, stand as much chance of being preserved as sand or mud-inhabiting species. All of these facts tend to show that L. litorea was not introduced from one continent to the other either at the same time or by the same means as L. palliata, and that if by any unknown agency what- soever L. litorea had reached America, it must have been con- fined to Nova Scotia alone until the middle of the present century. But we have another source of information about the shells which lived upon our coast before the advent of the Europeans. In the Indian shell-heaps along the coast of Maine and New Brunswick, most of the edible moUusks of the coast are found among the heaps of clam-shells. Dr. Wyman reports" that in a shell-heap at Crouch's cove, Casco bay, Maine, Littorina palliata * Forbes and Hanley's British MoUusca, Vol. ni. • Manual and instructions for the Arctic expedition. •Packard, Mem. Bost. Nat, Hist. Soc, Vol. i. ♦Can. Nat., 11, 408. » Can. Nat., i, 345. •Am. Nat., Vol. i, No. ii, 1868. London, 1876. 1 886.] Is Littorina liiorea Introduced or Indigenous f 937 ; sense in was found along with such species as Purpura lapillus, Naiica heros, Bticcinum undatum, Nassa obsoleta, Nassa trivittata, etc., but he makes no mention of L. litorea. Mr. G. F. Matthew, in his account^ of investigations into an undisturbed shell-heap on the shore of Passamaquoddy bay, New Brunswick, after men- tioning the occurrence of several littoral species, says : " The rock periwinkle {Littorina rudis) is occasionally found * * * but the common European periwinkle {Littorina litorea), now so common on this coast, is entirely wanting." In a private letter to the writer the same gentleman says : " I have seen no trace of L. litorea in any shell-heap." That the Indians would have col- lected the smaller native periwinkle and other small littoral spe- cies, and not the larger English one, were the latter present, is in- conceivable, no matter whether the former had been collected for food or only accidentally introduced into the shell-heaps. The same causes should have introduced L. litorea if it had existed at these places. Again the conclusion is forced upon us that if the shell existed in America at the time of the formation of the shell- heaps, it must have been confined to Nova Scotia. We have no published lists of shells from the Nova Scotia shell-heaps, nor has the writer been able to find by private inquiry any satisfac- tory account of them. All of the facts that we have so far mentioned in connection with this shell show that if it existed at all in America previous to the present century, it must have been confined to the coast of Nova Scotia. There are other general considerations which show that in all probability it did not exist there. One of these we have already mentioned — the fact that it was not introduced in the same way as L, palliata, by way of Greenland, and therefore was probably not naturally introduced into America at all. Many undoubtedly European species of both animals and plant could be named which, upon their artificial or accidental introduction into this country, have driven out and well-nigh exterminated closely-allied native species. Everywhere upon the coast of Nova Scotia as well as that of the rest of Acadia and New England, L. litorea is doing precisely this, driving out the native L. palliata. Everywhere the native form gives way before it and becomes rare, just in proportion as the English form becomes abundant. This fact of itself gives us strong a priori grounds » Bull. N. B. Nat. Hist. Soc, lu, 1884. 938 Is Littorina litorea Introduced or Indigenous f [November, t!! for believing the shell to have been recently and accidentally in- troduced, but it acquires additional force taken in connection with other facts which point to the same conclusion. But granting for a moment that the shell did exist in Nova Scotia previous to this century — where it must have been con- fined if it was in America at all — what an anomalous condition of life we have. At present, as we follow its progress southward, we find it growing more and more abundant. The writer has very frequently noticed its distribution on the Southern New Brunswick coast, but it there occurs in nothing like the profusion in which he has seen it at Nahant, Mass., or Ne wport, R. I. In these two places, and they are like other localities in these two States in this respect, it literally covers the rocks, the native spe- cies becoming comparatively rare. What is the meaning of the fact that it becomes more abundant southward ? Can it mean anything else than that (within certain limits) as it goes south it meets with a more and more congenial habitat ? If this be so, and we can see no bther conclusion, it shows that Z. litorea thrives better in warmer water than that of the coasts of Nova Scotia and New Brunswick, and therefore that the natural home of the species, or the place where it originated was in warmer water than that of Acadia. This conclusion is strengthened by the fact of its non-occurrence in Greenland or Labrador, to both of which places it should have been carried by the same agencies which took L. palliaia there. The latter is certainly a more northern species than the former, and it may be that the condi- tions of life in these two places are altogether unsuited to the more southern L. litorea^ in which case it could certainly not have been carried from one continent the other by way of Green- land. If then L. litorea existed upon the Nova Scotia coast as (in the sense in which we are using the word) an indigenous spe- cies, it was existing without spreading under comparatively un- favorable conditions of temperature, etc., while favorable condi- tions were waiting for it not far to the southward. Surely the agencies which took it from one continent to the other (if natu- rally introduced) could have carried it to the New England coast. Is it not more natural to suppose, what so many of the facts in- dicate, that the warmer waters in which it thrives the best are like those of its home, and that its home is in the waters of the English coast, which we know to be so much warmer than those of Nova Scotia ? jvember, itally in- nnection in Nova ;en con- idition of uthward, riter has em New profusion R. I. In hese two ative spe- ng of the n it mean 1 south it his be so, L. litorea 3 of Nova iral home n warmer ihened by r, to both agencies a more he condi- ed to the :ainly not of Green- a coast as nous spe- tively un- ile condi- lurely the (if natu- and coast, e facts in- best are rs of the han those 1 886.] Is Littofina litorea Introduced or Indigenous ? 939 But again, what is the meaning of its wonderfully rapid spread, and why, if it existed in Nova Scotia previous to say 1850, did it not begin to spread before? Its spreading as rapidly as it has,, shows that it was only waiting for the opportunity to take advan- tage of it, but why, if it is indigenous, did it not begin to spread sooner? Surely the same causes which have carried it south since 1850 were in operation before. If they were natural, such as currents, etc., they certainly have been present substantially unchanged for centuries. Professor Verrill suggests that it may have existed formerly in Nova Scotia, but have " become more diffused in recent times by commerce." But surely there was commerce between Nova Scotia and New England before 1868 (in which year it was first reported from Maine), and enough of it to satisfy the most exacting demands of this theory. In all probability the rapid diffusion of the shell since 1857 is in a measure due to both of these causes, but the fact that they did not have a like effect before, seems very strongly to show that the shell was not in Nova Scotia for them to spread. The waters which bathe the Atlantic coast of Nova Scotia are carried by the strong Fundy tides across to the New Brunswick and Maine coasts, and if currents had anything to do with carrying L. palli- ata from one continent to Greenland and thence to the other, it should have carried the free-swimming embryos of its ally, L. litorea, from the Nova Scotia to the New England coast. But grjanting again for a moment that L. litorea has existed in Nova Scotia for an indefinitely long time as an indigenous species, we have it existing under conditions very different from those in which it thrives in England, having, as has been shown, no con- nection with the latter, and yet retaining its specific identity. It is possible for a species to keep its identity in widely separated localities, where the conditions of life are not precisely the same, only by a continuous intercourse between the different localities. This is in all probability the case with L. palliata, for we find it ranging freely around the North Atlantic in England, Greenland, Labrador, Acadia and New England, and the agencies which carried it from one land to the other have in all probability been in operation ever since. But with L. litorea the case is differ- ent; if it existed in Nova Scotia it must have been cut off from all communication with England, and that it should retain its • We have found no list of the shells of Iceland. !IF f- i I 940 Is Liftotina litorea Introduced or Indigenous ? [November, specific identity under such conditions is altogether inconceiv- able. We have not been able to present any direct proof that L. lito- rea did not exist in Nova Scotia before the present century. The testimony of the nur^erous lists (by independent observers, who could not have overlooked the shell had it been present) of shells on the coast of New England and New Brunswick in none of which occurs any mention of L. litorea, the testimony of its absence from the Post-pliocene deposits of other {.irts of Canada where L. palliata (along with which it always exists) has been found, the testimony of the Indian shell-heaps, into which it would certainly have been carried by the same means or for the same purpose as was L, palliata, all of these combined afford almost absolute proof that the shell did not exist on the Atlantic coast of America outside of Nova Scotia. If these same tests could be applied directly to Nova Scotia the question would be settled as to whether it occurred there. An earh" list of the shells of that Province, or careful investigations into its Post-plio- cene deposits and Indian shell-heaps, would practically remove all doubt one way or the other. B".t the former does not exist and the latter has not been made. It must have existed in Nova Scotia, if at all. But at the same time its absence from Greenland and Labrador, v/here, in accord- ance with what we know of the geographical distribution of ani- mals, it ought to occur along with L. palliata if it is indigenous ; the extreme improbability of its remaining in such a small area without spreading, with causes in existence tending to carry it from a less favorable to a more favorable habitat ; and the impos- sibility of the species remaining isolated from the parent stock in England for an indefinitely long time, and yet in spite of quite a differently conditioned habitat remaining specifically identical with it, all of these facts tend to show that it did not exist even in Nova Scotia. Is not the conclusion warranted then, that Litto- rtna litorea is not indigenous to America, but has been recently and artificially introduced from Europe ? ^ i