CUTICLE, ETC., OF DISTOMUM 139 



fibre-like structure of the deeper layer of the cuticle stands 

 out very prominently. 



The hooks also show very plainly the structure of a 

 meshwork, and, moreover, of one that is modified into 

 longitudinal fibres throughout its whole extent, upon which 

 fact depends its longitudinally striated appearance.. Blue 

 granules are also deposited in its framework, although not 

 very abundantly. Numerous lacunar spaces, resembling 

 longitudinal clefts, appear in the substance of the hooks. 

 The latter do not project out freely above the cuticle, but 

 are completely embedded in it, being clothed up to their 

 pointed external ends by a cuticular covering which gradu- 

 ally thins out more and more. On the other hand, the 

 internal ends of the hooks project beyond the inner limit of 

 the cuticle into the body. Between the circular and longi- 

 tudinal muscles a protoplasmic framework extends, which 

 carries numerous granules, stained deep blue, in its nodal 

 points. Although I could not make out completely to what 

 cellular elements this framework properly belongs, and 

 especially whether the so-called gland cells, which appear so 

 abundantly under the musculature, do not in some way 

 belong to it, I would nevertheless draw attention to the fact 

 that the fibrous trabeculse of the framework of the cuticle 

 are continued quite distinctly into the protoplasmic frame- 

 work extending between the musculature. It seems to me, 

 therefore, to follow with certainty that the cuticle, together 

 with the hooks, has arisen by direct modification of a proto- 

 plasmic framework, although the actual origin of this 

 covering of the Trematode body appears still as doubtful as 

 ever. 



Very remarkable relations are shown also by the peculiar 

 and thick, so-called hacillar lining or cuticular border of the 

 epithelial cells' in the gut of this worm. The epithelial 

 cells have a very distinct meshwork, arranged to form 

 longitudinal fibres, and closely packed with blue granules, 

 on which account it is relatively dark. The deep bacillar 

 lining stains only a dirty light blue colour. If this lining 

 be studied in the thinnest possible tangential sections through 

 the epithelium (that is to say, in reality transverse sections 



