NO. 6 INSECT ABDOMEN — SNODGRASS II7 



of the isopod. The parap roots themselves Crampton regards as the 

 protopodites (i. e., combined coxopodites and basipodites) of the 

 terminal appendages. The interpretation of the paraproct lobes as 

 exopodites is consistent with other evidence that the styli are exop- 

 odites, for the paraproct lobes fall in line w^ith the styli, or would 

 do so if styli were present in the tridactylids, and the abdominal styli 

 are serially continuous with the thoracic styli of Machilis, which 

 appear to have an exopodite status, and therefore suggest that the 

 entire series of styliform organs are exopodites. 



There are several weak places in the above line of reasoning. In 

 the first place, the writer fails entirely to get Crampton's view from 

 the comparison between the tridactylid and the isopod, since, with 

 the terminal parts of both in the normal condition (fig. 45 B, D), 

 the cercus of the insect (Cer) surely has the position of the exopodite 

 {Expd) of the crustacean uropod, while the paraproct lobe (paptl) 

 corresponds in position with the small endopodite (Endpd) borne 

 by the basal plate of the uropod (C). In the second place, a more 

 careful examination of details shows that the cercus (B, Cer) has 

 no anatomical relation with the paraproct (Papt), being situated 

 dorsad of the latter in a position corresponding with that of the base 

 of the crustacean uropod (D). Furthermore, as has already been 

 shown, there is no evidence whatever to support the idea that the 

 paraprocts of insects are parts of the appendages. Their musculature 

 indicates that they are mere lateroventral, subanal lobes of the eleventh 

 abdominal sternum. The cerci have no muscles arising in the para- 

 procts. Finally, the embryological evidence concerning the nature 

 of the cerci appears to show definitely that the cerci are the entire 

 appendages of the eleventh segment, and that their bases, if present 

 at all, are retained in a basal ring of each organ. Hence, until some 

 radically new information comes to light concerning the cerci, there 

 is no question of exopodite or endopodite connected with them. Our 

 present information is to the efifect simply that the cerci are the appen- 

 dages of the eleventh abdominal segment. 



The lobes of the paraprocts, whether the " paraprocessi " of the 

 tridactylids, the small lobate ends of the paraprocts of the Anisoptera, 

 or the lateral gill plates of the Zygoptera, have no validated claim 

 to an appendicular origin. They must, then, for the present be re- 

 garded as secondary outgrowths of the subanal lobes of the sternum 

 of the eleventh abdominal segment, comparable to the various median 

 outgrowths of the supra-anal plate of the same segment. 



The most nearly convincing evidence of the biramous nature of 

 insect appendages is, admittedly, the presence of styliform processes 



