524 J. PERCY MOORE. [Vol. X. 



and, although naturally everted penes are not difficult to ob- 

 serve, the bursa is never displaced. The everted penis in such 

 cases is quite long enough to be functionally useful. In B. 

 philadelphicus, on the other hand, the penis and its sheath are 

 united into a solid piece, incapable of eversion, and here the 

 whole bursa, which has quite a different structure, is everted 

 naturally and carries the short projecting end of the penis with 

 it. The inner surface of the bursa is smooth in B. illuminatus, 

 and shows no trace of the elongated and more or less branched 

 papillae which are present in certain other species. 



The ovaries (Fig. i) consist of a pair of cell masses attached 

 one on each side to the septum ^-7, and hanging into the 

 coelom of the seventh somite. In immature individuals they 

 have the arrangement described by Voigt for Branchiobdella, 

 but are more slender, and are borne on longer muscular 

 pedicles. In the mature worm the ovaries have become much 

 more bulky and of irregular shape (Fig. i). Their mass is 

 made up of young ova (Fig. 27) of nearly uniform size. The 

 immature ova are spherical, with a large, clear nucleus and 

 distinct nucleolus. A transparent stroma in which the ova 

 are imbedded appears to be present, and the ova themselves 

 are arranged in irregular rows, showing the manner in which 

 they have proliferated and pushed out from the germinal epi- 

 thelium. Among the ova of the peripheral part of the mass 

 a few enlarged ones in the early stages of maturation are 

 always present, and two or three large irregular ones nearing 

 maturity. The latter have usually broken loose from the 

 ovary, and, as irregular masses, conform to the shape of the 

 perivisceral cavity, which they largely fill, closely enveloping 

 the intestine. A clear nucleus may always be detected in 

 living examples, in which the white opaque ova are very con- 

 spicuous. In such ova the nuclei have become very much 

 enlarged and somewhat vesicular. The entire cytoplasm is 

 filled with minute rounded yolk granules (Fig. 28, d), among 

 which a few deeply staining specks are scattered. During the 

 period of maturation the ova appear to receive nourishment 

 directly from the peri-enteric blood sinus, with the thin wall of 

 which they lie directly in contact. The pair of vascular arches. 



