316 STUDIES IN THE EVOLUTION OF ANIMALS 



the animal which gradually adapts its structure to surrounding 

 conditions, but that sometimes a monstrosity may occur which 

 with an abnormal structure must either adapt its habits to its 

 surroundings or must cease to live? Those monstrosities which 

 can succeed in adapting themselves to surrounding conditions live, 

 and reproduce themselves, to startle and puzzle us with the fact 

 that so many strange and abnormal structures are suited to 

 identical habits ! And so we have Ibises, Spoonbills, and Herons, 

 among Waders, leading the same life ; and Pigeons, Parrots, 

 Toucans, and Chatterers, among frugivorous birds, leading also an 

 identical life among trees. 



There seems no reason for doubting that a monstrous in- 

 dividual, having found its monstrosity useful in the battle of life, 

 would acquire in some cases habits consonant with the monstrous 

 limb or limbs , and we might be misled by thinking that the 

 anomalous structures were brought about by the habits gradually 

 modifying the structure, while the exact reverse may, in many 

 cases, have happened, just as an athletic man would take to athletic 

 habits because his muscles were originally well developed. 



That new habits, to which organisms may have been driven, 

 may be engendered by slow and minute steps of variation in 

 structure may be too true, but this in no way excludes the great 

 probability that many new and monstrous variations, as we 

 would now call them, may have originated in one great and sudden 

 step^ improving afterwards if the individual were viable and 

 reproducible. That anomalous structures are often supplied with 

 not only bones, but also muscles, vessels, and nerves, as if they 

 were inherited, and ready equipped for use, is sufficiently proved 

 by the supernumerary digits. In many cases, both structurally and 

 functionally, these could not be distinguished from the normal ones. 



1 Professor W. Kitchen Parker thought so also (Mammalian Descent, p. 93). 



