1922] Walker: Structure of Orthopteroid Insects 51 



probably the sinistral paramere in the Blattid Periplaneta, or 

 the Mantid Stagmoniantis, but the large dextral lobe is not cer- 

 tainly its fellow of the opposite side, but may belong to the 

 same lobe, since in the Mantids the sinistral lobe is greatly 

 developed and bears two processes or more, while the dextral 

 is greatly reduced. It may, therefore, be possible that both 

 hooks shown in the figure belong to the left side and that the 

 dextral lobe does not show or may be absent. 



Odonata. 



In the dragonflies the general elongation of the abdominal 

 segments includes the terminal ones, although the tenth is 

 small as compared with the others, except the first. 



The ninth sternum covers much less than the entire sternal 

 region of the ninth segment, there being a considerable area 

 posterior to the genitalia, which is morphologically part of 

 the membrane between the ninth and tenth sterna, though it 

 may be more or less chitinized and appears to be part of the 

 sternum itself. The genitalia thus appear to be situated upon 

 the ninth sternum rather than upon the succeeding intersternal 

 area. In other words the ninth sternum has not kept pace with 

 the elongation of the tergum and the genitalia thus appear to be 

 shifted cephalad. 



The ninth sternum is not modified as a subgenital plate, but 

 there are two small, flat plates on each side of the genital 

 aperture and partly overlapping it. In the nymphs of the sub- 

 order Zygoptera and in those of certain Anisoptera such as the 

 Aeshninae these plates are readily seen to be homologous with 

 the lateral gonapophyses (dorsal valves) of the female, as 

 pointed out by Van der Weele ('06), and are therefore coxites. 

 In the young nymphs of some Zygoptera vestigial styli are 

 borne at their apices, though these disappear later. 



In the ninth sternum is thus preserved the primitive 

 division into sternite and coxites. 



The genital aperture is surrounded by a chitinous ring and 

 may be slightly elevated upon a small papilla, but there is no 

 functional penis morphologically comparable to that of other 

 insects, the copulatory organs being situated upon the sterna 

 of the second and third segments and having no homology with 

 the genitalia of other orders. The problem of the origin of these 



