POLYCLAt) TUl;]!KI,LAl;lA. 129 



side there is, in addition to these, an inner diagonal layer, ami, lastly, an inner 

 longitudinal layer. 



Gut. The pharynx is large and folded, of the type usually found in Planoceroids. 

 The gut branches are very numerous and anastomose freely. The cells forming the 

 epithelium appear to have broken away, in most cases, from the gut-wall, and to have 

 rounded themselves into little spheres which lie free in the lumen. This is possibly 

 due to some delay in fixing the tissues after the specimen was taken from the dredge. 



Genital Apparatus. The ovaries are dorsal ; the testes cannot be distinguished in 

 my sections, although the ends of the vasa deferentia are crowded with spermatozoa. 

 The relations of the rather complicated terminal parts of the genital ducts will be 

 rendered more easily comprehensible by a reference to the accompanying Plate, 

 fig. 9. 



Terminal Male Organs. The small conical penis (pe.), which is unarmed, projects 

 into the antrum masculinum (a.m.), which is a simple chai.. 1 -r lined with what 

 appears to be a secreting, non-ciliated epithelium. Into the base of the penis run 

 two ducts : one, that lying more dorsally, conveying secretion from a small muscular 

 prostate gland (pr.), the other, the more ventral of the two, runs backwards and 

 downwards for some distance to widen into a vesicula seminalis (v.s.). This latter 

 duct is lined with ciliated epithelium and has rather thick muscular walls. It widens 

 rpiite gradually into the vesicula, which receives on its dorsal side, some way behind 

 its anterior end, the two vasa deferentia (v.d.), which, as they approach the vesicula, 

 become endowed with muscular walls, composed, as in the case of the vesicula and its 

 duct, of circular fibres. 



The prostate duct is very short and enters the prostate immediately after it 

 passes out of the penis. The interior of the prostate is divided into three longitudinal 

 chambers (see Plate, fig. 1) by the folding of its secretory wall, outside which is a 

 thick layer of circular muscle fibres traversed by a few radial and longitudinal 

 strands. 



Female Terminal Ducts. The vagina is chiefly remarkable for its extreme length. 

 The antrum {a.f.) is small, it opens vertically upwards. From it the vagina (ra.) runs 

 straight forward close to the dorsal body-wall. It consists here of a tube of rather 

 narrow diameter, lined with ciliated epithelium, and surrounded by a few circular 

 muscle-fibres. It continues forward until it has passed right beyond the level of the 

 male organs. Its diameter then increases and it bends downwards and forwards for 

 some distance, then turns upwards, receiving the secretion of the large shell glands 

 (sh.gl.) at this level. Finally, near the dorsal body-wall, it turns sharply backwards, 

 running parallel to the first part of its course and at about the same level with it, so 

 that the two parts often lie side by side. At a level considerably in front of the 

 extreme front end of the male apparatus the backwardly-directed part of the vagina 

 receives the common duct running into it from the two uteri (c.d.). This duct is 

 rather longer than is usual. The backward course of the vagina is continued until 



s 



