HENRY J. FRANKLIN. 225 



as levers over the apex of the female hypopygium as a common ful- 

 crum. The apical projection of the volsellse are absent in Psithyrus. 

 The hairy condition of the volsellse seems to indicate that they may 

 be of some use as sense organs. At the base of each, on the ventral 

 side and largely enclosed by the branch, is a small piece called, in this 

 paper, the nux (fig. 71, NX). 



(4) An elongate, usually slender, organ on each side, between the 

 claspers. These pieces are known as the sagittae (figs. 71, 119 and 

 120, H and Y). Their distal ends are variously modified in form 

 among the different species and usually have more or less strongly 

 recurved parts. The modified terminal portion of these organs is, in 

 this paper, called the head (figs. 71, 119 and 120, H), while the long 

 basal part is called the shaft (Y) . The sagittse are of great value in 

 the classification of species. As has been indicated in the discus- 

 sion of the female organs, their heads are plunged into the vagina 

 ahead of the penis, and serve to open it for the insertion of that organ. 

 When the sexual connection is fully established, separation is probably 

 very difficult in some species on account of the sagittal heads. It is 

 certain that the male organs are sometimes torn completely off from 

 the males in this separation. The heads of the sagittse, in most spe- 

 cies, are extended ventrad more or less strongly, and they often bear 

 some microscopic hairs. The sagittae attain their greatest complexity 

 of form in the Terrestris group. This, together with the noticeably re- 

 duced volsellse, the four-toothed female mandibles and the probably 

 almost universal subterranean nest building habit, marks this group as 

 the most specialized of all the bumble-bee groups thus far recognized. 



5. A median and dorsal organ known as the uncus. Radoszkowski 

 (Bull. Soc. Natural. Moscow XLIX, P. 1, 1884, p. 53) called this piece 

 the spatha, but I have seen fit to use that name for the two ventral 

 pieces making up the genital couvercle. The uncus is always narrowed 

 toward the distal end and this end is always curved strongly ventrad 

 (figs. 71, 73, 119 and 120, U). It varies greatly in width between spe- 

 cies. It overlays the bases of the sagittae. Its surface is smooth and 

 it is without hair. It appears to function as a protection and guide to 

 the penis. 



6. The penis is a flexible and membraneous organ which is deeply 

 retracted under the base of the uncus when not in use. Its distal end 

 is much enlarged. 



Certain parts of the male genitalia are modified abdominal 

 segments. Counting the propodeum as the first abdominal 

 segment, the cardo represents the ninth tergum, the outer 

 spatha the eighth sternum, and the inner spatha the ninth 

 sternum. The tenth segment appears to be absent as far as 

 any representation by chitinous plates is concerned. 



TRANS. AM. ENT. SOC, XXXYHI. (29) 



