42 



AN INSTANCE 

 OF MISGEGENATION IN THE GERRIDAK , 



(HEMIPTERA) 



bj II. AI. Paroihlcy, lie. D. 



It is évident that in the scheine of Nature the interbreeding of 

 species is iiot favoi-ed ; in other words, species are isolated, and 

 this isolation is accomplished by widely diverse means. In the 

 mammals there often seenis to be no anatomical or even instinctive 

 obstacle lo interbreeding and hence geographical and seasonal bar- 

 riers assume importance in Iceeping species separate at the maling 

 time. Tiius it appears thaï in the case of such animais two very 

 closely related species are seldom if ever fonnd to inhabit the same 

 territory, and the related dogma, that similar forms occurring in 

 separate ranges, such as différent valieys or islands, must be trea- 

 ted as distinct species, has perhaps been too fully accepted. 



In the insects species are likewise separated by geographical and 

 seasonal bai-riers in many cases, but Ihe entomologist can by no 

 means subscribe to the statemenl thaï closely related forms cannot 

 occur together, on the contrary numerous instances could be ad- 

 duced from any of Ihe orders. Under Ihese circumstances isola- 

 tion may be accomblished by either anatomical or psychological 

 means. It has been shown by the systematic sludies of récent 

 years that in many groups the chitinous portions of the genitalia 

 are of complex and even grotesque conformation, and the size and 

 shape of the varions parts may dilTer widely even in species other- 

 wise hardly distinguishable. If we examine, for instance, the maie 

 génital appendages in the species of Lygus or Pliytocoris, it is 

 évident that such diverse structures must bave corresponding 

 modifications in Ihe female for their accomodation, that the anato- 

 mical relation between the sexes of such species is well illustraled 

 by that between a lock and ils proper key. In olher cases the female 

 may exhibit the diversity more openly, while somelimes both sexes 

 show it clearly. Thus in certain groups of insects the species, 

 however similar they may be in other cliaracters, présent striking 

 genitalic traits, which serve to separate the species as surely in the 

 systematisl's cal)inet as they do in nature. That thèse génital cha- 

 racters should be employed as generic criteria only with extrême 

 caution and only when they are correiated with other important 

 structural diflerences, is suiri<:iently indicated by their function as 

 barriei's to the interbreeding of species. 



