182 



SCIENCE. 



[N. S. Vol. II. No. 33. 



had been formed. From last accounts the 

 little colony was doing well. This is but 

 one example of many which prove that 

 mollusks are distributed in this manner. I 

 have one authentic case of a number of 

 Anodons being carried away by a whirlwind 

 and falling several miles distant during a 

 severe rainstorm. 



Distrihution by human agencies. Man has 

 been a great factor in the distribution of all 

 animal and vegetal life, and the Mollusca 

 are no exception to the riile. The great 

 Erie Canal has been a powerful transporting 

 agent. In it we find species of Physa, 

 lAmncea and Planorbis, which were once sup- 

 posed to inhabit only the western lakes and 

 rivers. Even European species, like the 

 giant Limncca stagnalis, have been brought 

 over from Germany and France, and are 

 now found from Illinois to ISTew York ; so 

 also with several small Valvatas and Amni- 

 colas. Land mollusks have also been 

 brought from Europe, either adult or in the 

 egg, and we now have several colonies of 

 Helix nemoralis and H. hortensis in several 

 parts of the United States. In the City of 

 Mexico, in a little corner of the cypress 

 grove at Chapultepec, is a large colony of 

 Helix aspersa, which, up to the time of its 

 discovery, in 1890, was not supposed to be 

 found in Central America. It is now 

 spreading over the vallej' of Anahuac, and 

 will before long be a recognized part of the 

 fauna of Mexico. This species was un- 

 doubtedly brought to Mexico with German 

 goods, found a locality favorable to its ex- 

 istance, and has grown and multiplied. 

 This same species is now found in Charles- 

 ton, South Carolina ; New Orleans, Louisi- 

 ana ; Portland, Maine ; ISTova Scotia ; Santa 

 Barbara, California ; Haj'ti ; Chili ; etc. It 

 is a curious fact that Helix hortensis was 

 not accidentally introduced into the country, 

 as were H. nemoralis and H. aspersa, but was 

 first brought to Burlington, New Jersey, by 

 Mr. W. G. Binney. This species does not 



thrive so well, nor does it spread so rapidly, 

 as did the other species mentioned. 



Our large garden-slugs, Limax maximum 

 and L. agrestis, were introduced into this 

 country some fifty years ago, and are now 

 found all over the northeastern part of the 

 United States and parts of Canada. The 

 transportation of hothouse plants has been 

 the principal means of distributing these 

 species, for they are found more abundantly 

 in greenhouses than in any other locality. 

 Geological changes also tend to disperse 

 mollusks and also to change their mode 

 of living. A single example will suf- 

 fice to illustrate this point. In Africa 

 there is a lake (Lake Tanganyika) in 

 which live a number of mollusks almost 

 identical in the form of the shell and ani- 

 mal with the marine group of shells known. 

 as Trochids ; yet these mollusks live in 

 fresh water and have the principal charac- 

 teristics of fresh-water species. Now this 

 lake must at some time have been con- 

 nected with the sea, and the change from 

 salt to fresh water must have been very 

 gradual in order not to have killed off all 

 the animals. Numbers must have died 

 during the change, and those that were the 

 most enduring lived and multif)lied. The 

 result of the change is some of the most 

 curious mollusks known to science. (^lAm- 

 notrochus, Tiphohia, Neuthauma, Tanganyicia, 

 etc.) 



And thus I might go on and give hun- 

 dreds of examples of the distribution of 

 mollusks by natural and artificial methods; 

 but I believe I have given enough to illus- 

 trate my point, which is that there is noth- 

 ing so very wonderful in the finding of 

 species hundreds of miles from their sup- 

 posed natural habitat, and that the appar- 

 ent ' paradox ' of their discovery can be 

 accounted for by some one of the examples 

 given above. More attention should be 

 given to the careful recording of facts such 

 as those I have given, which are to my 



