The life histoiy of Diplodiscus temporatns Stapfokd. 599 



Digestive system. 



The moutli, which is situated at the centre of the anterior 

 sucking- disc, opens backward into two pharyngeal pockets, one on 

 either side. These are situated dorsally to the level of the mouth 

 cavity. Posteriorly the mouth cavity opens into the long" narrow 

 oesophagus, which extends backward about one third the length of 

 the body. At its posterior end there is a pharynx-like swelling 

 with comparatively thick muscular walls. This expanded portion of 

 the oesophagus opens into paired caeca. These extend along the sides 

 of the body nearly to the posterior sucking disc. 



The wall of the intestine is made up of a layer of large 

 vacuolated cells which rest on a thin basement membrane. Each 

 cell contains a large nucleus, which is situated in the basal portion 

 of the cell; where the cytoplasm is most homogeneous. From the 

 inner ends of the digestive cells there is a rather ill defined layer 

 of fine protoplasmic processes which extend into the lumen of the 

 gut. ZiEGLER (1883), Looss (1894), Tennent (1905) and other 

 investigators have described the same condition in the intestinal 

 epithelium of many trematodes. These structures are usually con- 

 sidered to be of some service in the absorption of food. 



Water vascular system. 



The main trunks of the water vascular system are clearly seen 

 in the living worm. The terminal cells (flame cells) are readily 

 demonstrated when a living worm is put under pressure beneath a 

 cover glass and examined after it has stood for from thirty minutes 

 to an hour. 



The excretory pore is situated on the mid-dorsal line just anterior 

 to the border of the posterior sucking disc. From this pore a short 

 canal leads forward and downward to the excretory bladder, which 

 lies in the dorsal part of the body between the ovary and the 

 acetabulum. In a living worm the excretory bladder may be seen 

 to contract rhythmically as long as the animal remains at all 

 active. 



The two main lateral trunks, one on either side, extend from 

 the bladder, at first laterally, until they approach the body wall. 

 Here each turns anteriorly and runs along beside the caecum of the 

 corresponding side. In its posterior half each main trunk is much 

 convoluted. The folding in my specimens was about equal in the 



