No. 3.] CLINOSTOMUM HETEROSTOMUM. 699 



with its contained eggs, as whitish masses. The body is flat- 

 tened and hollowed ventrally, the neck being more terete and 

 narrower, but also capable of being flattened and hollowed 

 ventrally. 



The anterior sucker is not large, but appears large from 

 being surrounded by a mobile lip made up of a protrusion of 

 the body wall. It is situated ventrally, slightly behind the 

 anterior extremity. The acetabulum, situated some distance 

 behind this, at the junction of the first and second thirds of 

 the body, is larger than the anterior sucker in my specimens. 

 At about the middle of the portion of the body behind the 

 ventral sucker, the genital openings are seen close together, 

 that of the female apparatus being directly in front of the male 

 opening. The skin is unarmed. 



The anterior sucker is situated on a slight eminence, and is 

 entirely surrounded by the lip, which seems to assist in the 

 physiological action of the sucker. The cavity runs upward 

 and backward, and narrows suddenly into the very short 

 oesophagus, which is provided with a muscular pharynx. The 

 musculature of the sucker is composed of three layers, meridi- 

 onal, radial, and equatorial, or arcuate. The pharynx, similarly 

 tonstructed and provided with a thick cuticular lining, opens 

 directly dorsally into the much pigmented intestine, which 

 branches almost immediately, sending the two coeca to the 

 posterior end of the body. These coeca remain simple, but 

 become much sacculated by the development of folds in the 

 walls. The musculature of the intestine is limited to a single 

 longitudinal layer. It is the arrangement of the mucosa with 

 its extensive pigmentation, however, that offers one of the most 

 striking characteristics of this species. The wall of the coe- 

 cum is thrown up into high folds resembling somewhat the 

 valvulae conniventes of the human intestine, and giving on 

 section, when the coecum is cut tangentially, a ladder-like 

 appearance. The epithelium is in a single layer, and consists 

 of very tall cells tapering somewhat toward the lumen of the 

 tube. These stain deeply at the base, where the rounded 

 nucleus is situated (PL XXXIX, Fig. 6), but not so well centrally 

 — possibly this appearance is partly due to their being thinner 



