the Genus Criissicaula. 



417 



structure or artificially prolufied by tli;i pressure of the male, 

 lie does not a|)[)ear to have seen specimens in the position of 

 copulation, nor did the 'Terra Nova' material tlirow any 

 ligiit on this point. From the constancy with which the 

 constriction ap[iears 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 vaoina (fij^s. 3 A and 4, va.), in both species, is very 

 short and muscular, and gives off, almost immediately in front 

 of the cauclal 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 



F ii,^ 6. 



O-i mm. 



Ova, (A) of C. boopis, (B) and (C) of Crassicauda sp. (?) from Hyperoodon. 

 (C) represents a later stage tliau (B), and shows the thickened 

 belt of chitin. 



direction of the head. The ova (fig. 0, A) have a very thick 

 shell, and in both forms measure about 50 /iX 35 /x. Tiiey 

 contain a coiled embryo when laid. 



As ri'gar<ls the anterior eiul previously described by the 

 wiiter (191G) as that of (!. crassicauili, 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 that it is C. boopis than C. crassicauda. The various 

 records of the occurrence of the supposed C. crassicauda were 

 collected in the same paper, and a list of hosts was given, 

 'i'liis, in view of the fact that the species of Crassicauda 

 cannot now be regarded as one, will require some revision ; 



