i()o8] Habits of Insects as a Factor in Classification 71 



groups of animals, but I wish especially to speak of this group. 

 No better- audience for such a subject could be possible than one 

 including so many who are devoting a large amount of valuable 

 time and effort to the perplexing problems of insect classification. 



Some twenty years ago our worthy president, Professor Corn- 

 stock, published a remarkably suggestive paper on Evolution and 

 Taxonomy in which he set forth in a masterly manner the idea 

 that what we believe in evolution should be used as a basis in our 

 taxonomic work, or that our systems of classification should show 

 the lines of evolution of the various groups. Since then some 

 papers have made good use of this general principle, but there 

 are still many groups in which current classifications have largely 

 ignored the principle or sadly distorted it in interpretation. 



Perhaps if we agree on the principle we have used unfortunate 

 methods in determining its application, and it is with the hope 

 of showing possibly a little more clearly one of the helps in deter- 

 mining this point that I propose to discuss the habits of insects 

 in connection with the possible aid they may give us in tracing 

 the lines of evolution. 



Primitive insects which we may conceive to have been largely 

 terrestrial in habit have diverged along certain main pathways 

 such as adaptation to aquatic life, underground existence, arboreal 

 life, sedentary condition, parasitic habit, gall making habit, and 

 a host of minor lines of special adaptation. To bring out their 

 significance we may best review somewhat hurriedly some of 

 these lines of divergence. 



SUBTERRANEAN LIFE. 



The tendency of insects to burrow underground is perhaps 

 one of the more primitive lines of adaptation, as it may very 

 easily be seen to come from their efforts at concealment, to escape 

 enemies, to avoid light, or in arid regions to escape excessive 

 heat, and in many groups as the simplest mode of pupation. From 

 the more general form, however, we find in almost every order 

 cases of especially adapted species or sometimes whole genera or 

 families including varying degrees of adaptation to underground 

 life. Mole crickets are the most perfectly adapted of the Orthop- 

 tera, but indications of the easy stages in this group arc shown 

 by crickets and stone crickets which are less perfectly fitted for 

 such life. A group taking these features into account would evi- 

 dently place the mole cricket as the extreme form in this line of 

 adaptation. 



