58 Annals Entomological Socieyt of America [Vol. XV, 



CONCLUDING REMARKS ON THE PHYLOGENY OF 

 ORTHOPTEROID INSECTS. 



In any attempt to unravel the relationships of a group of 

 organisms it is obvious that the entire structure of the body 

 should be taken into account. It would be beyond the scope 

 of this paper, however, to do this for the Orthopteroid orders 

 of insects, but it may be useful to examine the results of our 

 studies of the terminal abdominal structures from this point 

 of view, taking into consideration, at the same time, results 

 obtained and opinions held by other workers on various regions 

 of the body. 



Few will deny, I think, that the Pterygota are descendants 

 of either a single species of winged ancestor, or a group of nearly 

 related forms in which the wings were evolved under similar 

 conditions from homologous parts. The evolution of wings 

 is a unique and anomalous development in the Arthropoda, 

 and their invariable presence on the same two body segments 

 with the same fundamental structure and plan of venation 

 makes it exceedingly improbable that they have arisen inde- 

 pendently in more than one group of nearly allied forms. 

 Accepting this view, we must assume that there was a single 

 species of common ancestor of winged insects possessing either 

 wings or the appendages from which wings were evolved. 



It is also generally agreed upon that the Thysanura is a 

 primitively wingless group, as their general structure reveals 

 a number of features that are more primitive than those of 

 existing Pterygote insects. 



If these premises are correct it follows that where structures 

 or characters are found in both Thysanura and Pterygota, 

 that are undoubtedly homologous, these structures or char- 

 acters were present in the common ancestral Pterygote form, as 

 also in the common ancestor of the Thysanura and Pterygota. 



Thus, from what has been learned regarding the terminal 

 segments and genitalia of the Orthopteroid insects, we should 

 expect to find in the common Pterygote ancestor the following 

 characters : 



