328 TEE ZOOLOGIST. 



condition, it is a survival of original assimilative colouration, and not a direct 

 product of natural selection " (p. 473). The question to be considered is, 

 whether these propositions have been sufficiently maintained. 



I may here state that, so far as concerns the endeavours of some biolo- 

 gists to make natural selection responsible for every trifling detail of colour, 

 I can sympathise to some extent with Mr. Distant's general attitude ; as, 

 for instance, when it is attempted to explain trivial local variations by the 

 purely hypothetical and quite unprovable assumption that these are corre- 

 lated with certain obscure but useful constitutional characters, of which we 

 know nothing at all, on the ground that it is these characters, and not the 

 trivial colours themselves, that have been operated upon by natural selection. 

 Such contentions certainly do not commend themselve in the present state 

 of our knowledge. But when one contemplates the vast mass of valuable biolo- 

 gical work, both in arduous experiments and paisntaking observations, that has 

 been and is still being accomplished by the champions of natural selection 

 in order to test the validity of the Darwinian theory in every hole and corner 

 of the organic world, one can only read with unfeigned astonishment the 

 assertion that " the tendency to explain all problems by natural selection 

 is to-day greatly retarding the study of bionomics. It is not one whit re- 

 moved from the proferred explanation of the old teleologists, and represents 

 as little thinking "! An endeavour to refute this assertion would be out of 

 place here ; and I need only mention, with special reference to the last 

 phrase of the above quotation, that although the explanation on the selection 

 theory of the inter-resemblance of distasteful insects appears simple enough 

 at the present day, yet for twenty years it baffled the ingenuity of such 

 men as Bates and Wallace, until Fritz M tiller put forward the ingenious 

 theory of mimicry now associated with his name.* 



But to return to Mr. Distant's suggestions. We are at once confronted 

 with a difficulty in that no definition is offered of the exact significance of 

 the term " assimilative colouration," which is evidently loosely applied, see- 

 ing, for example, that the brilliant red on the wings of the African Touracos 

 is given as an instance of partial assimilative colouration (p. 460), f appa- 

 rently on the assumption that these birds eat copper J — the common copper 



* Of course Mr. Marshall does not suggest that Muller's theory has found 

 universal acceptance ? — Ed. 



t The exact passage to which exception is taken reads as follows : "This 

 cannot be taken as an instance of pure, but only partial, assimilative colour- 

 ation, but is sufficient to prove that colour may be largely derived from the 

 mineral constituents of the earth's surface, and in this way can scarcely be 

 altogether ascribed to the action of ' natural selection.' " — Ed. 



I The "assumption that these birds eat copper" is not found on the page 

 criticised ; and is negatived by a quotation given from Mr. Monteiro (p. 459). 

 —Ed. 



