Organic Evolution. 187 



unless the wing sprang into existence already sufficiently 

 developed for flight, this would be impossible. The same 

 is true of the first stages of many structures which could 

 not be of service for the purpose and use to which they 

 were subsequently turned. Not impossibly, the earliest 

 "wings" were for diving, and flight was, so to speak, an 

 after-thought. Undoubtedly, structures which have been 

 fostered under the wing of one form of advantage have 

 been subsequently applied to new purposes, and fostered 

 through new modes of adaptation. Teeth, for example, are 

 probably modified scales, such as are found in the thorn- 

 back skate. But the early development of these scales 

 could have had no reference to their future application to 

 purposes subservient to alimentation. 



Again, such and such a structure is sometimes spoken 

 of as a "prevision against emergencies." In his interest- 

 ing and valuable work on " The Colours of Animals," 

 for example, Mr. E. B. Poulton says, "Dimorphism [in 

 the larvae of butterflies and moths] is also valuable in 

 another way : the widening range of a species may carry it 

 into countries in which one of its forms may be especially 

 well concealed, while in other countries the other form may 

 be more protected. Thus a dimorphic form is more fully 

 provided against emergencies than one with only a single 

 form." And after giving, as an example, the fact that the 

 convolvulus hawk-moth has a browner and a greener form 

 of caterpillar, of which the browner is more prevalent 

 under European conditions, and the greener under those 

 which obtain in the Canary Islands, Mr. Poulton adds, 

 " This result appears to have been brought about by the 

 ordinary operation of natural selection, leading to the 

 extermination of the less-protected variety." Now, I do 

 not mean for one moment to imply that so careful and able 

 a naturalist as Mr. Poulton believes that any character has 

 been evolved through natural selection in prevision for 

 future emergencies. But I do think that his statement is 

 open to this criticism. 



(3) It is sometimes said, in bold metaphor, that natural 



