| OCR Text |
Show 426 DARWINISM OIIAP. produced by some other power, then nn.tural selection is not wanted. If, on the other hand, both fit and unfit a~·e produced, and natural selection decides between them, that _Is pur~ Darwinism, and Mr. Cope's theories have added nothmg to 1t. 1. 2. 9. 0 I ' r;:-=~ ~· FIG. 35.-Transforwation of Artemia salina to A. "Milhausenii; 1, tail-l ob~ of A. sa~in:, and its transition through 2, 3, 4, 5, to 6, into that of A. Mllhauscnll; t, post-abdomen of A. salina; 8, post-abdomen of a form bred in brackish water; 9, gill of A. :M:ilhausenii ; 10, gill of A. salina. (From Schumukc-witsch.) Semper on the Direct Influence of the Envi1·onrnent. Another eminent natur;a1ist, Professor Karl Semper. of Wurzburg, also adopts the view of the direct tramdonm ng power of the environment, and has brought together an XIV FUNDAMENTAL PROBLEMS 427 immense body of interesting facts showing the influence of food, of light, of temperature, of still water and moving water, of the n.tmospherc and its currents, of gravitation, and of other orgn.nisms, in modifying the forms and other characteristics of anima1s.1 He believes that these various influences produce a direct and important effect, and that this effect is accumulated by inheritance; yet he acknowledges that we have no· direct evidence of this, and there is hardly a sinblc case adduced in the book which is not equally well explained by adaptation, brought about by the survival of beneficial variations. Perhaps the most remarkable case he has brought forward is that of the transformation of species of crustaceans by a change in the saltness of the water (sec Fig. 35). Artcmia salina lives in brackish water, while A. Milhauscnii inhabits water which is much salter. They differ greatly in the form of the tail-lobes, and in the presence or absence of spines upon the tail, and had always been considered perfectly distinct pecic . Yet either was transformed into the other in a few generations, during which the saltness of the water was gradually altered. Yet more, A. salina was gradually accustomed to fro her water, and in the course of a few gcnerationR, when th' wu.tcr had become perfectly fresh, the species a was changed into Branchipus stag- I Fu:. 3G. nalis, which had always been considered to belong to a different genus on account of differences in the form of the antennre and of tho posterior segments of the body (see Fig. 36). This certainly appears to be a proof of change of conditions producing a change of form independently of selection, and of that change of form, while remaining under the same conditions, being inherited. Yet there is this peculiarity in the case, that n. Dranchipu s . lagna li s. b. Al'temia saliua. there is a chemical change in the water, and that thi W<ttcr permeates the whole body, and must be absorhcd by the tissues, and thus affect the ova and even the reproductive 1 The Natural Uonditions of E .. dstence as they Affect .Animal Ltfe. London, 1883. |
