STRUCTURE OF CLINOSTOMUM 195 



This fact corresponds with the statements of Mac Galium except 

 in so far as he gives the impression that these openings are located 

 on the outer surface of the body. The excretory, pore opens (as 

 shown in fig. 4) dorsally very near the posterior end of the body. 



THE STRUCTURE OF THE BODY WALL 



In general the trematode body is encased in a wall made up of 

 a non-cellular cuticula, which may or may not be spinous, rest- 

 ing upon an outer zone of the parenchyma in which muscles run 

 in various directions. For convenience we may consider the 

 oblique muscles as marking the inner boundary of the wall though 

 there is no break in histological structure at that point. The 

 fibers of the oblique muscles lie in groups considerably spaced 

 from each other so that the central parenchyma passes up be- 

 tween the muscles to the cuticle. This well-known structure is 

 shown by Braun in Fasciola hepatica ('93, pi. 29, figs. 1, 2 and 3); 

 it is also found in Cotylaspis (Osborn, '04, fig. 21) and in many 

 other forms. 



In Clinostomum marginatum there is a decided departure from 

 the usual type which, since a similar structure has not been re- 

 ported for any other trematode so far as known, merits a detailed 

 description. Figs. 3, 4 and 5 show the relation of the wall to the 

 body as a whole. The wall seems to be distinctly marked off from 

 the central substance in these figures, due to the prominence of 

 the large oblique muscles. 



The cuticle is as usual. It measures from 0.01 to 0.015 mm. 

 in thickness, is entirely structureless, is reinforced by spines which 

 ordinarily do not project beyond the surface. The spines are 

 acute and taper from a broader base seated on the deeper surface 

 of the cuticle. They are set close together. Twin spines of 

 smaller size sometimes occupy the position of one spine of ordi- 

 nary size, as if the amount of embryonic material apportioned to 

 one spine had been subdivided between two. Spines are found in 

 all parts of the general surface of the body, they are more numer- 

 ous on the ventral surface and on the posterior parts of the dorsal 

 surface. They are not found generally on the surface of the oral 

 field, with the exception of a small area immediately adjoining 



