440 W. A. HASWELL. 
this position always presents a colourless spot, owing to the 
absence, in the area directly over the antrum and female 
aperture, of the parasitic Algee, and also of pigment. The 
area is always depressed, and in it there is frequently to be 
recognised an appearance like that of aclosed cleft or fissure. 
In only a few cases was an actual opening observed. But 
the study of sections through this region shows that there is 
always, in sexually mature animals, an actual or potential 
passage, leading from the dorsal surface into the antrum. 
This appears most distinctly in sagittal sections, such as 
those represented in figs. 21 and 22, which are accurate 
copies of photographs. In all series of sections of speci- 
mens with ripe ova this cleft or passage is to be de- 
tected. This observation must have an important bearing 
on the question of the functions of the various parts of the 
reproductive apparatus, and will be referred to later. In the 
meantime I will point out that this passage, if not homo- 
logous, is at least closely comparable with the ‘canal of 
Laurer” of Trematodes. 
Near its dorsal extremity the antrum, or, more correctly, 
the passage which continues it forwards and dorsad, gives off, 
nearly at right angles, the two ducts of the bursz. These are 
lined externally with a continuation of the muscular layer of 
the antrum; but they have no regular epithelium, containing 
instead a somewhat irregular layer of cells, which does not 
bound a definite lumen, but has running through it several 
narrow passages. Those passages, and the lumen of the 
vagina, often appear blocked with the secretion of the uni- 
cellular glands. 
Each of the lateral ducts into which the antrum divides 
terminates in the corresponding bursa seminalis (0. 8.). 
The wall of this is composed of the same kind of material as 
the wall of the duct—a thin layer of muscle (fig. 18, 6. s.’) 
surrounding a mass of cells in which the remaining parts of 
the bursa are enclosed. Outside this is a thin layer of cells, 
the nuclei of which resemble those of the unicellular glands 
that surround the antrum. The bursa encloses the chitinous 
