356 H. s. PRATT, 



of 0.004 mm. It bears no spines but is ringed with the circular 

 grooves and ridges peculiar to most appendiculate Distomes. The 

 appendix is not ringed. These ridges and grooves, as Juel (1890) 

 has shown, merely represent superficial differences of thickness of the 

 outer layer of the integument and do not extend through it to its 

 inner surface; they appear in a longitudinal section as a serrated 

 line, the projecting edges of which are directed towards the hinder 

 end of the animal (PI. 25, Fig. 2). They are also most prominent in 

 the middle of the body becoming rounded and gradually disappearing 

 towards the hinder end and being smaller and blunter at the forward 

 end. The cuticula of tlie hinder end of the animal is destitute of 

 ridges and is smooth. The number of ridges in the larger animals is 

 about eighty-five. 



The integument or cuticula is composed of two distinct layers of 

 nearly equal thickness (PI. 25, Fig. 4). These two layers have been 

 observed in a large number of Trematodes (see Braun, 1892, p. 591; 

 also Looss, 1894, p. 113), among which are the appendiculate Disto- 

 mes (Juel, 1890, p. 9). They stain quite differently with different 

 stains. Both Looss and Juel report that the outer layer takes a 

 deeper stain than the inner. I find this to be true when safranin or 

 eosin is the stain used (PI. 26, Fig. 9): Ehrlich's haematoxylin, on 

 the other hand, stains the inner layer the more deeply (PI. 26, Fig. 7). 

 Between the two layers is often seen in sections stained with any 

 stain a sharp, deeply staining line. Juel finds that the inner sur- 

 face of the cuticula of Apdblema excisum stains very deeply with 

 haematoxylin (he fails to specify what one) and calls the layer thus 

 indicated the "intermediate layer" (intermediäre Schicht). I find such 

 a layer in certain parts only of the worms I examined : it is faintly 

 present in the hinder part of the trunk and very distinct in the ap- 

 pendix (PI. 26, Fig. 6). 1 am of the opinion that it only appears 

 where there is a considerable development of muscles, and is caused 

 by the strain of muscles on the inner surface of the cuticula. The 

 presence of the powerful retractor muscles of the appendix, which 

 are situated in the hinder part of the body, would account for the 

 formation of the "intermediate layer" in this place. 



Both layers of the cuticula usually appear perfectly homogeneous 

 in my preparations and contain no vesicles, concretions, nucleus-like, 

 or other structures. I have, however, usually found the outer surface 

 of worms which were still within their hosts, covered with irregular 

 vesicular or granular structures which roughened the surface of the 



