1922] Walker: Structure of Orthopteroid Insects 17 



majority of forms each hermitergite bears a more or less hook- 

 like copulatory appendage, but these may differ very greatly 

 in form and position. In Oligotoma saundersii, e. g., the dextral 

 hook is much longer and differently shaped from the sinistral 

 one (PI. I. Figs. 9 and 10). 



The ninth sternum is entire and without styli, and, except 

 in Clothoda, is asymmetrical, the apex being well to the left 

 of the median line and bearing another copulatory process. 

 The asymmetry also involves the cerci, which are two- 

 segmented, without including the basipodites. These sclerites 

 are generally inconspicuous, but in Clothoda they are well 

 developed, extending mesad in the form of freely projecting 

 plates, somewhat suggestive of the paraprocts of certain 

 Plecoptera, such as Perla. One might, in fact, be tempted to 

 interpret the latter as greatly enlarged cereal basipodites rather 

 than as true paraprocts. In Oligotoma the left basipodite 

 bears still another copulatory appendage on its inner side. 

 These various copulatory appendages converge on the left 

 side of the middle line, their position suggesting that in copula- 

 tion the abdomen of the female is grasped by the male from the 

 right side. 



Of the supra-anal plate, paraprocts and penis I have been 

 able to find nothing in Oligotoma. They must be extremely 

 vestigial if present at all, although the paraprocts are quite 

 distinct in the females of this order. 



It is altogether probable that the special characteristics 

 of the male Embiids, i. e., the asymmetry and the development 

 of the various copulatory appendages, have been evolved within 

 the history of the group itself, since its most primitive living 

 member, Clothoda, is lacking in these very features. Accepting 

 this view it is useless to attempt to homologise these processes 

 with those of similar function occurring in other orders. 



The male genitalia of the Embiidas offer little or no evidence 

 as to their relationships with other orders, but there is nothing 

 in their structure to conflict with the view held by MacLachlan, 

 Crampton and others that their nearest affinities are with the 

 Plecoptera. In fact, in the development of copulatory append- 

 ages from a great variety of parts, they at least show similar 

 tendencies to the Plecoptera, especially in the division of the 

 tenth tergum into hermitergites, each bearing a hook, a feature 

 which has already been noted in the case of the Plecopteran 

 genus Arcynopteryx, and is by no means confined to that genus. 



