CAPT. F. W. HUTTON ON" THE PROBLEM OF UTILITY. 331 



which are capable o£ recognizing tliem by the senses. Colour 

 can only be recognized by sigbt : consequently colours in animals 

 without eyes are not recognition-marks. But in some groups of 

 blind animals colour constitutes a specific character, as in the 

 shells of Lamellibranchs ; in these cases, therefore, it must be 

 either adaptive or non-utilitarian. Sculpture might possibly be 

 recognized by touch ; but we cannot suppose that in the Mollusca 

 the sexes recognize each other in that way, although ornament, 

 and slight differences in shape of the shell, constitute their chief 

 specific characters. Even with animals possessing eyes there are 

 some specific characters which cannot be regarded as reeogaition- 

 marks, for they cannot be seen ; as, for example, the teeth on the 

 radula of Gastropods. The venation of the wings in Lepido- 

 ptera and Trichoptera is obscured by scales or hairs, and yet it 

 often furnishes good generic and sometimes specific characters ; 

 occasionally even the venation differs in the two sexes. Some 

 crabs are always covered with seaweeds, and the species cannot 

 be ascertained until these seaweeds have been removed. And, 

 generally, obscure characters cannot be explained as recognition- 

 marks where there are conspicuous characters to answer that 

 purpose. Many species of Orthopterous insects differ from each 

 other in the number or position of the spines on the legs, and no 

 one will suppose that the male of one of these insects stops to 

 count the number of spines on the legs of a female before making 

 love to her. These specific characters, therefore, are not recog- 

 nition-marks. Are they adaptations ? 



Adaptations are of two kinds : those which are useful to their 

 possessor, and those which have been useful to former ancestors. 

 We can eliminate the last group by taking only the specific cha- 

 racters of a species the habits of which agree with those of other 

 species of the genus to which it belongs ; for in these cases the 

 habits must have remained the same during the whole of its 

 specific life, and the specific characters must, ex hypothesi, 

 have been developed by their present possessors. Wow can we 

 suppose that the colours which distinguish the shells of the 

 different species of Tellina, which live in sand, have any adaptive 

 value ? Can we suppose that a spine more or less, or a difi'erent 

 arrangement of the tubercles, on the carapace of a crab has any 

 adaptive value ? Can it matter in the struggle for life whether a 

 vein in the wing of an insect branches once or twice ; or can 

 slight differences in the number or position of the spines on the 



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