STUDIES OX TIJE ECTOPAEASITIC TREMATODES OF JAPAX. 9 



granules are also observable. In all tlie other species, the subcuticle 

 shows only granules, which are, however, more numerous in some 

 than in other species. For instance, in Microcotyle, Axine, Blmocotijle, 

 Diclidojihora, and Hexacotyle the granules are comparatively sparse, 

 while in Tristomum they are very numerous and exceedingly fine in 

 certain regions, e.g. on the ventral side of the anterior suckers. 



Inward to the subcuticle comes the basement memhrane. In cross- 

 sections it is very deeply stained, and very distinctly separable from 

 the subcuticle but somewhat less so from the subjacent mesenchyma. 

 Its thickness can not be measured with any accuracy, but it is always 

 thicker than the cuticle. Hallez'^ has shown with regard to plana- 

 rians, that the basement membrane is of the same natui'e as the dense 

 layer of connective tissue that surrounds the internal organs. Gene- 

 tically therefore it belongs to the mesenchyma rather than to the 

 investing membrane, and it is only in accordance with custom that 

 I have described it as forming one of its layers. 



In Tristomum sinuatum and Trist. ovale there are numerous 

 papillae on the surface of the body. These are of two kinds. Those 

 of one kind are mostly perceivable with the naked eye. In Trist. 

 simiatnm- they are confined to the dorsal surface of the body, and 

 measure on the average about 0.028 mm. in height, the extremes 

 being 0.014 mm. and 0.041 mm. ; the larger ones appearing to the 

 naked eye as granulations. In Trist. ovale, on the other hand, they 

 are confined to the ventral side where they are very numerous, and 

 are much larger than in Trist. sinuatum, measuring on the average 

 about 0.08 mm. in height, the extremes being 0.032 mm. and 0.122 

 mm. The papillae of the other kind are all microscopic and are far 

 less numerous than those of the first kind. In Trist. ovale they are 



1). HaJlez — Embryogenie des Dendrocoeles d'eau douce, 1887. p. 78. 



