[114] See especially, Koch, _Die Raupen und Schmetterling der Wetterau_, and _Die Schmetterling des Südwestlichen Deutschlands_, whose very remarkable results of numerous and varied experiments are epitomized by Eimer, _Organic Evolution_, Eng. Trans. pp. 147-153; also Poulton, _Trans. Entom. Soc._ 1893. Again, I may mention the remarkable case communicated to Darwin by Moritz Wagner, of a species of _Saturnia_, some pupae of which were transported from Texas to Switzerland in 1870. The moths which emerged in the following year were like the normal type in Texas. Their young were supplied with leaves of _Juglans regia_, instead of their natural food, _J. nigra_; and the moths into which these caterpillars changed were so different from their parents, both in form and colour, "that they were reckoned by entomologists as a distinct species[115]." [115] Mivart, _On Truth_, p. 378. With regard to mollusks, M. Costa tells us that English oysters, when turned down in the Mediterranean, "_rapidly_ became like the true Mediterranean oyster, altered their manner of growth, and formed prominent diverging rays." This is most probably due to some change of food. So likewise may be the even more remarkable case of _Helix nemoralis_, which was introduced from Europe to Virginia a few years ago. Under the new conditions it varied to such an extent that up to last year no less than 125 varieties had been discovered. Of these 67, or more than half, are new--that is, unknown in the native continent of the species[116]. [116] Cockerell, _Nature_, vol. xli. p. 393.