J22 TREMATODES. PHYLUM PLATYHELMINTHES 



its occurrence is perhaps connected with the nature of the food ; 

 it is present also in the urine of the highly carnivorous and largely 

 blood-feeding cats. The chief nitrogenous product is ammonia. 



NERVOUS SYSTEM 



The nervous system includes a brain which consists of a collar 

 around the pharynx with a mid-ventral swelling and a pair of 

 lateral sweUings. From these swellings or gangha nerves are 

 given off to the forepart of the body, and from each lateral 



ganglion arises a large 

 lateral nerve cord which 

 runs backwards below the 

 gut to the hinder end of 

 the body, giving off 

 branches on the way. The 

 nerve cords contain nerve 

 cells as well as fibres. 



GENERATIVE ORGANS 



The liver fluke is 

 hermaphrodite, and has 

 very complex generative 

 organs (Fig. ^y). The 

 testes are two much- 

 branched tubes lying one 

 behind the other in the middle part of the body. The branches 

 of each are gathered into a vas deferens, and the two vasa 

 deferentia run forwards side by side to join, above the 

 posterior sucker, a large, pear-shaped seminal vesicle. From 

 this a fine, somewhat twisted tube, the ejaculatory duct, 

 passes forwards to enter a stout, muscular penis or cirrus, which 

 opens at the generative pore. Normally the penis lies in a cirrus 

 sac, but it can be turned inside out and thus thrust out of the 

 pore. The ovary is a branched tubular structure on the right side 

 in front of the testes. Its branches join to form the oviduct, which 

 passes towards the middle line and there joins the yolk duct. 

 This is formed by the union of two transverse ducts, which lead 

 each from a longitudinal duct at the side of the body. The yolk 

 glands are very numerous, small, round vesicles lying along the 



Fig. 86. — Two flame cells, highly magnified. 



