1922] Walker: Structure of Orthopteroid Insects 7 



been termed a coxosternum (Verhoeff, '03). Coxosterna bearing 

 styli occur in the Blattoidea, Mantoidea, Isoptera and the 

 Orthopterous family Tettigoniidae, while coxosterna without styli 

 are present in the Dermaptera, Plecoptera, Embiidina and many 

 other Orthoptera, besides various orders not considered here. 



The 10th sternum is generally indistinguishable in the adult 

 state, but in many Plecoptera, Phasmoidea and Odonata it is 

 chitinized, though often not distinctly marked off from the 

 tergum, so that the segment is ring-like. In some cases at least 

 (Phasmoidea, Odonata) this appears to be a secondary chitiniza- 

 tion, correlated with the secondary elongation of the segment. 

 Chopard ('17) maintains that the inferior or infero-external 

 surfaces of the paraprocts also belong to the 10th sternum, 

 while the superior or supero-external surfaces represent the 

 11th sternum, this view being based (1) upon the fact that the 

 tergum of seg. 10 articulates with the lateral margins of the 

 paraprocts, and (2) that these two surfaces of the paraprocts are 

 often separated from one another by a distinct angle and may 

 differ in coloration or degree of chitinisation. It is true that 

 the 10th sternum becomes "absorbed" in the ventral faces 

 of the paraprocts, as has been determined in various species 

 of Orthoptera by one of my students. Miss Norma Ford, who is 

 engaged in a study of the abdominal musculature of Orthop- 

 teroid insects, but the 10th sternum does not form the entire 

 ventral surface of the paraprocts and sometimes only a very 

 small part of it. 



Chopard ('17) first regarded the supra-anal plate as the 

 tergum of seg. 11, but in his later and more extensive work ('20) 

 he accepts Heymons' view that an eleventh segment is present 

 in the embryo, between the 10th and the supra-anal plate. 

 But, whereas Heymons believes that no part of the 11th 

 segment persists after embryonic life, except the cerci, Chopard 

 considers the sternum of that segment to be represented in 

 the paraprocts, as described above, and considers the supra- 

 anal plate to be a telson, without a sternal counterpart. As my 

 own investigations have been confined to the study of the 

 postembryonic stages I have nothing of value to contribute 

 towards the solution of this problem. I may point out, how- 

 ever, that the paraprocts do not represent the sternum of 

 Heymons' 11th segment, and if this segment is recognized at 

 all it should be recognized in its entirety, including both tergal 

 and sternal regions. 



