STUDIES ON THE DIGENETIC TREMATODES, 413 
surface of the body, and consists of a large number of small 
cells closely aggregated and composing a fairly distinct body 
to external view. 
The common yolk-duct joins the oviduct between. the 
entrance of the ductus receptaculi and the ootype. The yolk 
reservoir lies just behind the shell-gland and is median. It 
forms a more definite swelling than Blanchard indicates. It 
is formed by the junction of the two transverse yolk-ducts. 
The longitudinal ducts run parallel to the intestinal diverticula 
and along their ventral surface. The yolk-glands consist of 
two lateral groups of follicles extending continuously from 
the level of the pharynx to the posterior end of the body. 
Behind the. posterior testis they extend in towards the middle 
line and fill up the posterior part of the body. In addition 
offshoots are sent in between the testes and in front of the 
anterior testis, and these almost unite in the middle line, 
thus separating the testes from each other and from the 
uterus. There is no tendency towards proliferation in front 
of the ventral sucker, the lateral fringes having a fairly con- 
stant width. Their situation is particularly towards the 
ventral surface, so that laterally they lie ventral to the 
intestinal diverticula and posteriorly. they do not approach 
the dorsal surface to any great extent. The follicles are 
irregularly ovoid and measure ‘08-10 by ‘04-06 mm. Each 
contains about a dozen gland cells, which present two distinct 
appearances. In each follicle there is almost invariably one 
cell situated centrally (fig. 4) differing from the surrounding 
cells in shape and staining reaction. This central cell 
appears to be free, not much compressed by the neighbouring 
cells, and in consequence has a regular oval outline. The 
remaining cells are closely pressed together into various 
polyhedral shapes. The staining reaction is more distinctive. 
The stain used was weak bemalum with aqueous eosin, but 
corresponding results were obtained with combinations of 
heematoxylin, methylene blue, and saffranin. The peripheral 
cells take on a uniform purple colour, while the central cell 
appears pink with acircumferential granular zone. ‘The nuclei 
