SEA-FISHERIES LABORATORY. 143 



distribution is represented in PI. III. In fig. 3 the 

 convolutions are represented diagrammatically to secure 

 clearness. For the same reason the eggs have been 

 omitted in both figures. The uterus passes forward over 

 the ventral sucker, at first side by side, and then dorsal 

 to, the seminal vesicle. It contracts greatly in diameter 

 in the neighbourhood of the latter structure. Here, and 

 here only, the uterus is muscular. Just over the prostate 

 gland there is a sphincter muscle (fig. 2), the contraction 

 of which usually reduces the calibre of the uterus to 

 much less than the diameter of an ovum. In fig. 2 this 

 sphincter is represented as a long-drawn-out structure, 

 but in other sections I have seen it as a short, thick, flat 

 ring of muscle fibres. This indicates that there are pro- 

 bably also longitudinal muscle fibres present, though it is 

 difficult to see these. The structure functions doubtless 

 in the extrusion of the ova. 



Immediately in front of this sphincter muscle the 

 calibre of the uterus enlarges, and we have a fairly wide 

 chamber which is the genital cloaca (fig. 2). In this, 

 as the figure shows, there are usually a few eggs. The 

 opening on the surface of the body is circular. Into the 

 terminal part of the genital cloaca there opens the cirrus 

 pouch, and usually the cirrus itself protrudes from the 

 latter, and out from the genital aperture on to the 

 surface of the body. 



The vitellaria are very characteristic. In a cleared 

 preparation they appear to ramify over every part of the 

 body, obscuring most of the other organs. This is par- 

 ticularly the case at the posterior extremity, where the 

 vitelline glands appear to fill up the whole body. But 

 in section they are seen to be arranged peripherally, 

 generally as a single stratum of gland follicles. At the 

 middle of the body they are dorsal and lateral. In front 

 h 



