MIMICRY. 3 



" At the best," he says, " we can reach only a probable inference." 

 Even in the most indubitable cases of adaptation, c.;/., those that 

 occur in the striking protective coloration of butterflies, the sole 

 ground of inference that the species upon the whole is adequately 

 adapted to its conditions of life, is that the species appears to be pre- 

 served undiminished, and, even then, we may not infer that this 

 protective colouring has selective value, nor that, if it were absent, 

 the species would necessarily have perished. At the same time Weis- 

 mann points out that many of the cases of protective coloration which 

 insects now exhibit, may not be at all necessary for their preserva- 

 tion at the present time, since, in some cases, a change in environ- 

 ment, in others, the extinction of an enemy against which they were 

 protected, may have taken place. In these cases, " the protective 

 coloration will continue until the law of organic inertia" {i.e., the 

 slow retrogression of superfluous characters) or new adaptations shall 

 modify it. 



It is suggested above that the control of nature in her minutest 

 details is gainsaid us, and, even if this be so, yet Weismann considers 

 that to renounce the principle of selection or to proclaim it as subsidiary 

 on the ground that protective coloration is not really protective colora- 

 tion, but a combination of colours inevitably resulting from internal 

 causes, " is to sacrifice the gold to the dross," for the " protective 

 colouring remains such," whether or not it be now useful to the 

 species, and " arose as such." In Weismann's opinion, the colour- 

 ing did not arise because " it was a constitutional necessity of the 

 animal's organism, that here a red, and there a white, black, or yellow 

 spot should be produced, but because it was advantageous, because it 

 was necessary for the animal." He assumes that only selection offers 

 an adequate explanation, and asserts that " we have no reason to 

 assume teleological forces in the domain of natural phenomena." 



Weismann then contrasts the position of those who argue that the 

 spots and patterns of a butterfly's wing have been wholly determined 

 by forces arising within the organism, and his own opinion that they 

 have been determined by utility. He says : — " It has been frequently 

 asserted that the colour patterns of a butterfly's wing have originated 

 from internal causes, independently of selection and conformably to 

 inward laws of evolution. Eimer has attempted to prove this asser- 

 tion by establishing, in a division of the genus Paidliu, the fact that 

 the species there admit of arrangement in series according to design." 

 Accepting this as a fact, Weismann asks whether " a proof that the 

 markings are modified in definite directions during the course of the 

 species' development, is equivalent to a definite statement as to the 

 causes that have produced these gradual transformations?" He further 

 asks whether " our present inability to determine with exactness the 

 biological significance of these markings, and their modifications, is a 

 proof that the same have no significance whatever?" Weismann then 

 states his belief that the wing of a butterfly " is a tablet upon which 

 nature has inscribed everything she has deemed advantageous to the 

 preservation and welfare of her creatures ; that the colour patterns 

 have not proceeded from inward evolutionary forces, but are the result 

 of selection. At least," he adds, " in all places where we do under- 

 stand their biological significance, these patterns are constituted and 

 distributed exactly as utility would desire." 



