xxxii, '21] ENTOMOI.OCICAI. \K\YS 250 



out in one plane (Fig. 11) in the position assumed by the 

 uropods of the crustacean shown in Figs. 14 and 15, the resem- 

 blance between the structures of the insect shown in Fig. 11 

 and the crustacean shown in Figs. 14 and 15 is very striking. 

 Thus, on either side of the terminal tergite labeled r/ 1 in Hg. 

 1 1 ( which apparently corresponds to the terminal tergite labeled 

 cp in Figs. 14 and 15) is a basal plate, pr, which correspond^ 

 in every way to the basal plate labeled pr in Figs. 14 and 15; 

 and the basal plate pr of Fig. 11 bears an inner appendage, en, 

 which is evidently the homologue of the inner appendage en 

 borne on the basal plate pr of Figs. 14 and 15. while the outer 

 appendage, r.r, of the plate pr of Fig. 11 is evidently the homo- 

 logue of the outer appendage of the plate pr of Figs. 14 and 

 15. I would therefore maintain that the basal plate, pr, or 

 paraproct, of the insect shown in Fig. 11, represents the proto- 

 podite of a crustacean's uropocl (i. e., pr of Figs. 14. 15, 16. 

 etc.), while the cercus. en, of the insect shown in Fig. 11 repre- 

 sents the endopodite, en, of the crustacean's uropod (. e., en 

 of Figs. 14 and 15), and the insect's paraprocessus. ex, (Fig. 

 11 ) represents the exopodite of a crustacean's uropod (i. e., ex 

 of Figs. 14 and 15), as should be evident to anyone who 

 examines the forms in question. 



Having determined the significance of the parts in an insect, 

 we are now in position to apply the knowledge thus gained, to 

 solving the question of the interpretation of the terminal struc- 

 tures of odonate naiads (immature stages) which was the 

 subject of a long dispute between Handlirsch, 1903-4, and 

 Heymons, 1904, and has not been correctly understood by the 

 students of the Odonata. In 1 leymon's case, a lack of 

 knowledge of comparative anatomy apparently prevented hi- 

 interpreting the facts of development aright, while T Tamil irsch 

 did not at first realize what adult structures \\ere derived from 

 the larval ones, and was later forced to the unnecessary and 

 unwarranted assumption that there is a re- formation ot the 

 cerci in odonate development, unlike anything occurring in 

 any other known insects. A comparison of the terminal struc- 

 tures of the odonate larva shown in Fig. S, \\ith those of tin- 

 insect shown in Fig. 4, very clearlv shows lliat the structure 



