24 BI'LLETIN 63, UNITED STATES NATIONAL MUSEUM. 



Homology. — The examination of the male reproductive organs of 

 nydroj)Mhis triangularis (Plate 9, figs. 1 and 2) suggests the homol- 

 ogy between the reprodiicti^'e organs in the Eleodiini, and also be- 

 tween the former and those of the latter. 



In Hydrophihis the edeagophore consists of a basale (Plate 9, fig. 

 Id) and two apical valves. The basale is impressed along the me- 

 dian line dorsally and is more or less membranous at that point, and 

 it therefore appears to have been developed by the partial coalescence 

 of two latei'al sclerites, termed by Packard the outer Johes; the tw^o 

 apical lobes he terms the inner lohes (Plate 9, fig. la), they are valvu- 

 lar in character and capable of free abduction and adduction; be- 

 tween them is the edeagus. 



I consider the outer lobes homologous with the basale, and the 

 inner lobes with the npicale in the Kleodviiii. 



If fig. 1 of Plate 9 be compared with fig. 12, Plate 2, a similar 

 structural condition of the valves in the two sexes and in very Avidely 

 separated series will be observed. It is evident that in Hydro philus 

 there has been less sexual difterentiation than in the Eleodiini^ and 

 also if the male characters of the latter be considered. 



The female genital segment of Hi/drophilus (Plate 9, fig. 10) ])re- 

 sents a complicated arrangement of sclerites which are noticeably 

 divergent from anything observed in the Eleodiini^ and nuist be 

 considered as a more primitive condition, in this agreeing with the 

 male characters. 



It has been made known by Nussbaum that unpaired parts like 

 the edeagus, etc., have been developed from paired ectodermal out- 

 growths which have fused together, and in all probability there, is 

 analogy between these outgrowths in the Insecta and those observed 

 in the Vertebrate Series; if this be so, then there must at some period 

 have been an indill'erent stage in the development of these organs, 

 and a time of beginning sexual differentiation. 



It appears to me that the apical lobes of HydropMlu^ and the api- 

 cale of the KleodUni are homologous with the genital segment of the 

 female. In Ilydrophilus there are the tAvo valves capable of free 

 abduction and adduction with the edeagus between and protected by 

 them; in the fenude of the Eleodiini the two valves are as capable of 

 free movement as in the above and enclose and protect the sexual 

 orifice. 



In the female the valves articulate with lai-ge paranal plates; in 

 the male the valves or apicale articulate with the outer lobes or basale. 

 and the paranal plates are small and articulate with a Y-sha]KMl 

 chitinous structure that is internal, the basal process of the basale 

 articulating with the arms of the Y by ligaments. 



