75 



field naturalist who is also an observer knows how excel- 

 lently every insect in all its stages fits into the conditions of 

 its environment. He also knows that if the insect exists 

 under varying conditions of environment a modification 

 takes place, the modification really understood by the term 

 " local race " applied to such instances. He has also 

 noticed that it is the characters which are of service to the 

 species under particular conditions that are most strongly 

 developed, and that modification takes place in a direction 

 (or directions) useful to the species. The usefulness of these 

 characters is the salvation of the species, for it is the 

 acquisition of these characters that allows them to fill a 

 place in the economy of nature, from which they cannot be 

 ousted by competitors or killed off by enemies. That there 

 is no real distinction between races and species is certain, 

 the matter often resolving itself into one of opinion, e. g. 

 Tephrosia crepiiscularia and T. historiata, Anthrocera trifolii 

 and A. lonicerce, A. vicice and A. charon, and so on. It is 

 only that such races or species are not yet so absolutely 

 separated in all their characters, structure, organs, function, 

 habits, &c., as are the older species which have been 

 isolated through vast ages of time ; and the criterion of 

 fertility inter se which is sometimes used to determine 

 whether a certain form is a local race or distinct species 

 would scarcely lead the entomologist to label Saturnia pyri 

 and S. pavonia, or Smerinthus ocellatus and S. populi, or 

 A mpliidasys strataria and A . hetularia, or Ennomos alniaria 

 {aiitumnaria) and E. quercinaria as species respectively. 

 And really, when it comes to the crucial point of what is a 

 " useful specific character," is it not largely a matter of 

 what individual judgment would label useful .'' We have no 

 very certain diagnostic characters in Leiocampa dictcea and 

 L. dictceoides, but we are all agreed that they are distinct 

 species because they have independent life cycles, are 

 specialised to different food-plants, have larvae that are 

 clearly distinguishable, and present a small detail or two of 

 difference in the arrangement of the imaginal markings. 

 Yet, in spite of the closeness of their affinity, there 

 can be no doubt that the two insects fill independent places 

 in the economy of nature, and that every detail (even of habit) 

 of the larva and imago is of importance ; that the very 

 essence of the perpetuation of two species apparently so 

 closely allied is the fact that they do fill independent places, 

 that they are differently constituted, and so have become 

 specialised in different ways, each succeeding where probably 

 the other would fail. 



