1922] Walker: Structure of Orthopteroid Insects 61 



the number of tarsal joints has been secondarily reduced, 

 while in some the ovipositor has become vestigial or absent. 



In this assemblage of groups there are two types of genitalia 

 so distinct as to indicate with some probability two main lines 

 of divergence. In one of these we have the true Orthoptera, 

 in which the primitive bilateral symmetry of the penis has been 

 retained, but the organ has acquired a peculiarly complex 

 structure very distinct from that of any other group. In the 

 earliest representatives of this line (Protorthoptera?) there was 

 undoubtedly a well-developed ovipositor without styli; a sub- 

 genital plate was formed in the female from the 8th sternum 

 and in the male from the fused coxites, which in all but the 

 branch leading to the Acridoidea, united also with the 9th 

 sternite. Styli were present in the males of primitive forms. 

 The cerci were probably short and unsegmented or had few 

 segments (as indicated by Tridactylus, in which the two-jointed 

 cerci may be a secondary feature). The tarsi may have been 

 5-jointed in the earliest forms, as suggested by many Tetti- 

 goniidce, but in all modern species the actual number of joints 

 is 4 or less. The primitive plecopteroid form of body was 

 apparently lost at an early stage, correlated with the develop- 

 ment of saltatorial hind legs. 



The second type of male genitalia is seen in the Phasmoidea, 

 Grylloblattoidea, Blattoidea, Mantoidea and Zoraptera (?), 

 and was doubtless present in the forbears of the Isoptera. 

 This type of genitalia is asymmetrical and consists of the 

 ejaculatory duct, sometimes borne upon a penis, between two 

 unequally developed lobes or processes, right and left, which 

 probably represent the parameres. The sagittal plane is 

 usually so shifted that the right lobe overlies the left. Associated 

 with this type of genitalia is a distinct tendency towards the 

 reduction of the supra-anal plate. 



These peculiarities are least marked in the Phasmoidea, 

 which probably separated first. In this group many of the 

 primitive Plecopteroid characters have been retained, par- 

 ticularly in the cervical sclerites, propleura, small and widely 

 separated coxae, and in the presence in such primitive forms as 

 Timema, of well developed intersegmental sclerites in front of 

 the meso- and metaterga (Crampton, '19). The cerci became 

 short and lost their segmentation, while the male coxites fused 



