414, WILLIAM NICOLL. 
also differ. In the peripheral cells they appear to consist 
of three concentric layers. The outmost zone is granular 
and stains deep blue, the middle is white, while the central 
part, the nucleolus, stains bright red. In the central cell, on 
the other hand, the nucleus stains uniformly bright red and 
appears to consist of little more than the nucleolus, The 
cells measure ‘02—03 mm. in diameter, while the nuclei 
measure ‘006-0075 mm., but those of the peripheral cells 
appear to be slightly larger than that of the central cell, 
The central cell is obviously the most mature part of the 
follicle, and it is probable that only in this condition are the 
yolk-cells despatched from the follicles. The yolk-ducts and 
reservoir, at any rate, contain only such cells. In their 
passage down the yolk-ducts they «ure compressed into a 
cubical or short cylindrical shape; in the reservoir they 
become polyhedral, but they again become cubical on passing 
into the common yolk-duct. They retain their bright red 
nuclei throughout, and these are still conspicuous within the 
most mature ova. No intrinsic muscle-fibres or true epithe- 
lium of the yolk-follicles or yolk-ducts could be observed, but 
this does not prove their absence as they are particularly 
difficult to demonstrate. 
Turning back from the ootype the uterus describes a 
moderate number of convolutions in the space between the 
posterior border of the ventral sucker and the anterior border 
of the anterior testis, Laterally it is confined by the 
intestinal diverticula, Owing to its thickness the ovary 
is not overlapped by the uterus. The convolutions tend 
towards and cause bulging of the ventral surface of the body. 
The terminal part of the uterus runs straight forward on the 
right side of the cirrus-pouch and passes into the vagina at 
the level of the posterior end of the pouch. ‘The vagina is 
also straight and has the usual muscular structure. Its 
diameter is ‘019 mm. in the undilated condition. The 
cuticular lining is ‘004 mm. thick. The thickness of the 
combined muscular layers is ‘003 mm, and the diameter of the 
lumen is only (005 mm. ‘To admit the passage of the ova it 
