STUDIES OX THE ECTOPAKASITIC TREMATODES OF JAPAN. [) \ 



each a .single iiucleolu^, u.s in Microculijlc chiri (IM. Y, fig. 4), 

 il/, sciaeiiœ (IM. VI, fig. i>), and (Juchocotiik spimicis (PL XM, 

 fig. (S). It seems to me therefore clear that the structureless membrane 

 of the vas deferens (^f most species is to he regarded as the transform- 

 ed product of the originally cellular epithelium ; and this becomes the 

 more pr(jba-ble when we see that nuclei are present in some parts of 

 the uterus but are wholly absent from others, as will l)e described later 

 <)n. In those species in Avhich the wall of the vas deferens consists 

 ordy of a structureless membrane there is often a coarsely granular 

 layer on the inner surface of the wall, wliich will be described pre- 

 sently in treating of the prostate gland. In most species the 

 vas deferens is wh(3lly destitute of any musculature ; but in some, as 

 in Mkrocotijlc sciacuœ (PI. VI, fig. 2) and HcxacoiijJc (PI. XII, fig. 5), 

 it is provided with a single layer of circular filjres. 



In ]\Ionocotijle there is a peculiar organ around the vas deferens at 

 a short distance from where this opens outwards (PI. XVII, fig. 1 

 & PI. XVIII, fig. o, hul. cj.). It is spherical in shape, is holhjAv, 

 and is traver.sed by the vas deferens. The wall of this organ is very 

 thick, and consists of connective tissue fibres Avhich are all arranged 

 radially ; it is bounded both internally and externally Ijy a structure- 

 less membrane ; but the external membrane is incomplete f )r a short 

 space on the dorsal side, and here the substance of the wall is directly 

 continuous with the surrounding mesenchyma, — the one passing 

 oTacluallv irito the other — thus showinir that both are (_)f the same 

 nature. On the surfice of the internal limiting membrane there is a 

 thin granular layer ; and just externally to the same membrane there 

 is a layer of circular muscular fibres (PI. XVIII, fig. 3, huL cj.). The 

 only use that I can attribute to this organ is to eject the sperm, 

 and I shall therefore call it hidJnis cjaculatoriu^. Around it there 

 is a circular canal, the plane of which coincides with that of 



