1922] Walker: Structure of Orthopteroid Insects 65 



APPENDIX TO PART I. 



There are a few matters discussed by Chopard ('20) in his 

 excellent treatment of the female genitalia of the Orthoptera, 

 on which my views do not quite coincide with his. The most 

 important of these are the following: 



Origin of the "pileohis'' and subgenital plate in the Tetti- 

 gonoidea and Grylloidea. Chopard contends that the subgenital 

 plate in these groups develops, not from the 8th sternum (ster- 

 nite) but from the membrane between the 8th and 9th sterna. 

 His observations on Pholidoptera femorata Fieber agree closely 

 with mine on Ceuthophilus and Conocephalus and his conclusions 

 are reasonable, but it appears to me unnecessary to give up the 

 view that the subgenital plate is formed from the 8th sternum. 

 According to Chopard the 8th sternum is already, at the 2nd 

 nymphal stage, reduced to two lateral pads, one at the base of 

 each ventral valve. During subsequent growth these become 

 shifted more and more laterad and finally form the small 

 triangular plate, which is termed by Chopard the "pileolus" 

 (valvifer). The subgenital plate appears at the third nymphal 

 stage in the form of a pad, or fold, arising from the membrane, 

 which separates the base of the ovipositor from the 7th sternum. 

 This view seems to imply that the "genital pocket," under the 

 subgenital plate, is an infolding of the membrane, but it 

 appears to me to be formed rather by an infolding of the 8th 

 sternum itself, which is quite flexible in the young nymph; so 

 that, according to the latter view, the subgenital plate may be 

 interpreted as an outgrowth from the basal part of the 8th 

 sternum. The greater part of the sternal area is thus represented 

 by the lining membrane of the genital cavity. This view is sus- 

 tained by Miss Ford's findings in her study of the musculature 

 of the parts in question, which are as yet unpublished. The 

 two parts considered by Chopard to be the vestiges of the 8th 

 sternum are the structures for which I have employed Cramp- 

 ton's term " basivalvula " and are, of course, quite properly 

 assigned to this segment. But, although they do become 

 shifted laterad, as Chopard states, they clearly do not become 

 the pileolus or valvifer. This is derived from that part of the 

 9th sternal area which lies laterad of the bases of the dorsal 

 valvulae. Even in the adult the intersegmental groove can be 



