#* AND ^'^/^ 



JOURNAL OF VARIATION. 



Vol. VIII. No. 4. June 15th, 1896. 



MIMICRY. 



III. — Utility as the predominant factor in developing mimetic 



PATTERNS. 

 By J. W. TUTT , F.E.S. 



In our preceding remarks (aiitr, pp. 31-33) we have attempted, to 

 show by what process of reasoning Weismann has reached the con- 

 clusion that utility is the mainspring in producing the particular 

 forms of protective coloration and mimetic patterns that we so 

 frequently observe, and we find ourselves agreeing with him that 

 utility does show us why these have been evolved each in its special 

 direction. 



We now find Weismann asserting that the " supposed formative laws 

 are not obligatory," and that " dispensations from them can be issued and 

 are issued whenever utility requires it." Weismann has previously stated 

 that, in his opinion, " the laws involved " in giving rise to the 

 markings are "the physiological conditions of the variation," and 

 that " the laws come into consideration only to the extent of con- 

 ditioning the quality of the constructive materials — the variations, 

 out of which selection fashions the designs in question." 



His assertion, therefore, is so startling that it may be well to con- 

 sider how he justifies it. He states that " these transgressions of the 

 law extend so far, that, in the very midst of the diurnal butterflies, is 

 found a genus, the South Xmevicnn Ai/fntnia, which, like the nocturnal 

 butterfly, shows on the entire upper surface of both wings a pro- 

 nounced bark-coloration, and concerning which we also know (and in 

 this respect it is an isolated genus, and dift'ers from almost all other 

 diurnal butterflies), that it spreads out its wings when at rest like the 

 nocturnal butterfly, and does not close them above it as its relatives 

 do." 



From this illustration Weismann concludes that "the facts here 

 cited are alone sufficient to remove all doubt that not inner necessities 

 or so-called formative laws have painted the surface of butterflies' 

 wings, but that the conditions of life have wielded the brush." 



We fail here to follow Weismann's reasoning, or to see how his con- 

 clusion at all follows from the principles that he has enunciated. We 

 can understand very well from the illustration that he gives, that 

 selection has brought about a certain useful result very satisfactorily, 

 but that the result has been arrived at independently of the laws 

 which he himself lays down (and which we quote in the second 



