458 W. BLAXLAND BENHAM, 
of the preceding segments except that it is much larger, and 
extends through some five or six segments. Rosa terms this 
the “ pseudo-prostate.”’ 
The minute structure of the clasper has been described by 
Rosa, and my observations agree very closely with his, though 
I cannot distinguish so definitely as he does the divison of the 
enclosed chamber into two by an imperfect horizontal septum. 
Nevertheless two regions of the cavity are readily dis- 
tinguished in transverse sections (figs. 17, 18); one portion 
of the lumen (C) is lined by close-set columnar cells, the 
other (A) by gland cells intermixed with ordinary cells, some 
of which are empty, and others filled with secretion (fig. 
19, gl.). 
The rest of the organ is muscular, with more or less abundant 
blood-vessels distributed through it. When the cavities are 
traced out it is found that the portion C is continuous with 
that surface of the protruded organ which is directed inwards 
(ventral), whilst the epithelium lining A covers the outer 
surface of the organ. The epithelium is everywhere one cell 
deep; there is no basement membrane, and the blood-vessels 
(fig. 19) pass up between the cells. In the section through 
a part of the protruded chamber the part labelled B (fig. 17) 
is, of course, the prominent organ seen in figs. 4 and 5, which 
was the specimen sectionised, and corresponds to Rosa’s 
*‘gyande scudo ovale,” which projects downwards from the 
roof of the upper chamber. 
The duct of the gland enters that region of the lumen 
marked C; its secretion, therefore, is discharged on the inner, 
ventrally directed face of the organ which is presumably 
used to grasp the other worm during copulation. Deeper 
in the organ the two cavities become continuous as in 
fig. 18. 
The two sperm-ducts of one side, after passing backwards 
along the body-wall on the medial side of the prostates, reach 
the “bursa,” and pass along its medial border. They then 
bend round it posteriorly, and enter the muscle surrounding 
the neck of the gland (pr*.); here they turn forwards and 
