218 [March, 



however, afterwards quotes from Kirby — " As we do not know the 

 value and weight of the momenta by which climate, food, and other 

 supposed fortuitous circumstances operate upon animal forms, we can- 

 not point out any certain diagnostic by which in all cases a species 

 may be distinguished from a variety ; for these characters that in some 

 are constant, in others vary." 



I believe that continuous interbreeding of individuals during a 

 succession of generations affords a true test of what constitutes a 

 species. Unfortunately, from the conditions of the existence of 

 insects this test is of very limited application ; and we have then only 

 analogy, experience, and observation to guide us. And seeing that by 

 rearing insects we have discovered not only that species, or rather the 

 individuals constituting them, vary inter se to a vast extent through all 

 their stages, but also that two species in their ultimate form are so 

 much alike as to present scarcely an appreciable difference, although 

 known to be derived from larvje of entirely distinct structure, habits, 

 and origin, it concerns us not hastily to decide from the imago state 

 alone that an insect is, or is not, specifically distinct. Under the 

 breeding-test, colour, marking, and size have been proved to have no 

 regular specific value in any stage of the existence. Dimorphism in 

 form of wings has been found to exist contemporaneously in the 

 same species {Lejjidopte7'a); in more than one Order one sex is winged 

 and the other apterous ; or there are macropterous and brachypterous 

 forms of each or either sex ; and there is good reason to believe that 

 the form of the thorax differs greatly in the same species, being cor- 

 related with alary development {Heviiptera). In Hemiptera, Dr. 

 Puton maintains that another structural difference exists in the same 

 species, and if he be correct in his hypothesis, many so-called species 

 will have to be ranked, at the most, as races induced by special cir- 

 cumstances, and which may or may not endure, and be established 

 eventually as true species, not breeding with other forms./ 



Dr. Puton contends* that pilosity, in certain injects at least, 

 is not a specific character, although it has been used to make 

 species. Thus, he says, that in the genus Salda, pilosella, Thoms., 

 is only a pilose form of S. palJipes, Fab. ; S. Cocksi, Curt., a 

 northern hispid form of S. geminnta, Costa ; ^S*. clegantida, Fall., the 

 brachypterous hispid form of S. cincta, H.-S., which is macropterous 

 and glabrous. "It is true," he continues, " that S. cincta has the an- 

 tennje notably thinner than S. ehgantula, but perhaps there is in this 

 a relation between the thickness of the antennas and development of 



■* Bulletin Soc. ent. France, IbTt', p. 205. 



