1896.] ^11 [Goddard. 



the possibility that the penis is to be regarded as the fused and greatly 

 modiiied abdominal appendages of the third abdominal segment. The 

 hamules of Plathemis also afford us a suggestion of the way in which 

 the branched maj^ have arisen from the simple condition. 



Conclusion : While my work has been mainly description, there are a 

 few general suggestions which may be thrown together here. 1. There 

 seems some reason for believing that the hamules are homologues of 

 abdominal appendages. 2. Various stages are observed between the 

 ordinary bifid condition of the hamules and the uniramous condition of 

 other subfamilies. As we have no reason to believe that the abdominal 

 appendages were originally biramous, we must suppose the condition in 

 Libellulinse a secondary one. 3. It has been impossible to homologize 

 the appendages of the penis- tip, though there seems some reason to 

 think that wider study might enable one to do it. 4. The resemblance 

 between these appendages in Diplax vicina and ruMcundula is very 

 close ; Celithemis elisa is quite different in some respects. This species 

 was formerly jslaced in the genus Diplax ; the marked difference and 

 the general similarity of the penis-tip is what we should expect in two 

 genera so closely related as to have been formerly classed as one and 

 leads us to believe that the study of this organ may prove to be of sys- 

 tematic importance. In conclusion, I wish to acknowledge the valuable 

 aid given me by Prof. M. A. "Willcox in the preparation of this paper, 

 both in general suggestion and revision. I have found no literature 

 which was of value save Rathke's paper, "De Libellarum Partibus 

 Genitalibus." 



Desckiption of Diagrams, Plates XIV akd XV.* 



Diplax ruMcundula. 



Fig. 1. One-half of tergum. 



Fig. 2. Second segment — ventral view. 



Fig. 3. Framework, triangle, and hamules. 



Diplax meiiia. 



Fig. 4. Second segment — -ventral view. 



Fig. 5. Framework, triangle, hamules, and sternum. 



Fig. 6. Genital bladder and side-view of penis, 



■Celithemis elisa. 



Fig. 7. Second segment — ventral view. 



Fig. 8. Framework, triangle, hamules, and sternum. 



Fig 9. Genital bladder and penis — dorsal view. 



Lihellula exusta. 



Fig. 10. Second segment — ventral view. 



Fig. 11. Framework, triangle, hamules, and sternum. 



Fig. 12. Genital bladder and side-view of penis. 



* The scale by wliich drawings were made differs, but as size in mm. is given, there 

 need be no misunderstanding. 



