the Genus Crassicauda. 417 
structure or artificially produced by the pressure of the male, 
he does not appear to lave seen specimens in the position of 
copulation, nor did the ‘Terra Nova’ material throw any 
light on this point. From the constancy with which the 
constriction appears in females of all sizes, it seems probable 
that it is a preformed structure, and not merely due to the 
act of copulation itself. 
The vagina (figs. 3 A and 4, va.), in both species, is very 
short and muscular, and gives off, almost immediately in front 
of the caudal constriction, two uteri, which are thick-walled 
and have a narrow lumen. ‘These, after forming one or two 
coils, run, parallel to each other and nearly straight, in the 
Vie. 6. 
O-/ mm. 
Ova, (A) of C. boopis, (B) and (C) of Crassicauda sp. (?) from Hyperoodon, 
(C) represents a later stage than (B), and shows the thickened 
belt of chitin. 
direction of the head. The ova (fig. 6, A) have a very thick 
shell, and in both forms measure about 50 4x35. They 
contain a coiled embryo when laid. 
As regards the anterior end previously described by the 
writer (1916) as that of C. crasstcaudu, it is not at present 
possible to decide to which of the two species here distin- 
guished it belongs. From its size alone it appears more 
probable thatit is C. boopis than C.crassicauda. ‘The various 
records of the occurrence of the supposed C. erasstcauda were 
collected in the same paper, and a list of hosts was given. 
This, in view of the fact that the species of Crassicauda 
cannot now be regarded as one, will require some revision ; 
