52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. OQ 



tettigoniid type. Walker says that " in the external form of the val- 

 vulae and their connections with neighboring sclerites Grylloblatta is 

 remarkably like a primitive Tettigoniid, such as CeufhophHus." The 

 three pairs of valvulae are well developed, but the dorsal and ventral 

 pairs are not connected, and the median pair is exposed between them. 

 The basivalvulae form distinct sclerites between the bases of the ven- 

 tral valvulae and the eighth sternum. Crampton believes that the basi- 

 valvulae are derived from the " coxites " of the eighth segment of the 

 nymph, but he gives no evidence that the sclerites in the nymph are 

 limb base elements. The presence of well-developed styli on the ends 

 of the dorsal valvulae in the nymph of Grylloblatta, which are lost 

 in the adult, is a primitive feature retained likewise in the young 

 of Blattidae. 



GRYLLUS ASSIMILIS FABRICIUS 



Since the cricket is a good subject for school laboratory work, it is 

 here selected for a detailed study of the orthopteroid abdomen and 

 ovipositor. The abdomen of the cricket gives a fairly generalized 

 example of the typical structure of the abdominal part of the insect 

 body. The ovipositor, however, is by no means generalized ; it is 

 specialized in the way the ovipositor of all Orthoptera is specialized, 

 and in addition it is one of the most highly perfected egg-laying 

 mechanisms found among the insects. 



The visceral region of the abdomen. — The pregenital segments of 

 the cricket's abdomen are all well developed in both the male and the 

 female (fig. 14 A), and contain distinct tergal and sternal plates. The 

 terga (T) are separated from the sterna (Stn) by a wide membranous 

 or coriaceous area on each side of the body, containing the spiracles. 

 Running lengthwise through each of these membranous areas, below 

 the spiracles, is a prominent lateral fold (a-a). The relations of the 

 parts of the abdomen above and below the lateral fold to each other 

 and to the corresponding parts of the thorax attest that the fold marks 

 the site of the dorso-pleural line. The membranous area above the 

 fold, containing the spiracles, is, therefore, the laterodorsal region, 

 or paratergal area of the dorsum (Id), and that below the fold is the 

 true pleural area (P). Anteriorly it is seen that the line of the dorso- 

 pleural fold on the abdomen extends into the thorax dorsal to the 

 thoracic pleural plates, or subcoxae (Sex), and that the pleural area 

 continued from the abdomen here expands between the metathoracic 

 tergum and sternum (T3, StUs) to include the thoracic pleura, or sub- 

 coxal parts of the leg bases. Posteriorly the line of the dorso-pleural 

 fold extends, in the female (B, a), between the tergum of the ninth 



