STUDIES OX TtiE ECTOPAEASITIC TREMATOt)ES OF JAPAX. 133 



seminis of Hcxacotijh i.s nothing' but a part of tlie genito-intestinal 

 canal, juîst as in Trislomum it i.s a part of the vaginal canal. The small- 

 ness of the seminal receptacle and the greater length of the canal pro- 

 ceeding from it towards the intestine observed in Hexacotijlc grossa as 

 compared with H. acuta is perhaps due to the fact that the sperm mass 

 was comparatively small in the specimens of the former examined; 

 for in H. acuta I have observed the seminal receptacle to vary con- 

 siderably in size, and the small canal to vary in length; the size of the 

 receptacle and the length of the canal being complementary, the 

 receptacle being formed inferentially, at the expense of the canal. 

 The fact already mentioned that in H. acuta the small canal proceeds 

 from the seminal receptacle sometimes in one direction and some- 

 times in the other also points to the same interdependence; the 

 cramming of the receptacle with sperm mass and its consequent 

 len^rtheninir causino: displacement of the "^enito-intestinal canal. 



The wall of the canalis (jcnUo-intcstinalis is formed of a thin, 

 structureless membrane, whose inner surface is uniformly covered with 

 fine cilia, the motion of which is distinctly obser^■able in living sj^eci- 

 mens under the microscope. It is wholly destitute of nuclei. In 

 Microcotijle and Axinc the wall is thickened circularly at sh(jrt intervals 

 just like the wall of the Laurer's canal in some species of D/.sfo;H?//;i 

 descriljed by Poirier;'^ only the thickenings are here much smaller 

 and nearer one another. In oblique or longitudinal sections of the 

 canal these thickenings look somewhat like septa, but that they are 

 not really such is very clear on attentive observation. In a surface 

 view these thickenings appear like circular muscular fibres. 



As to the opening of the canal into the intestine, it is to be noted 

 that it is exceedingly small and in most cases never appears in more 



1). Poirier— Z. c, p. 577. 



