ANNALS 



OF 



The Entomological Society of America 



Volume XII DECEMBER, 19 19 Number 4 



THE TERMINAL ABDOMINAL STRUCTURES OF 



ORTHOPTEROID INSECTS: A 



PHYLOGENETIC STUDY. 



By E. M. Walker, Toronto, Ont. 

 INTRODUCTION. 



There is still much difference of opinion concerning the 

 inter-relations of the various orders of insects, particularly 

 of the so-called "lower" orders, and even the question as to 

 what are the limits of these orders is by no means a matter of 

 general agreement. 



If these problems are ever to be solved in a logical manner, 

 all the available data must be taken into account. The evidence 

 afforded by comparative anatomy, ontogeny and palaeontology, 

 or any facts bearing upon the subject, must all be fairly con- 

 sidered. Although much information has been accumulated 

 from these various sources, there are still important fields 

 which have received much less attention than they deserve. 

 In the field of external morphology the greatest advances 

 have been made in the study of wing-venation, which, thanks 

 to the classical labors of Comstock and Needham, now rests 

 upon a thoroughly sound basis; the mouth-parts have also 

 long been a favorite subject for investigation, w^hile in com- 

 paratively recent years, good progress has been made in the 

 study of the thoracic and cervical sclerites, particularly by 

 Snodgrass and Crampton. 



Our knowledge of the terminal abdominal structures, 

 especially the genitalia and associated parts, is still, however, 

 in a very unsatisfactory state. A constantly increasing value 

 is being attached to them by systematists in separating genera 



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