30 THE LIVER-FLUKE. 



B. The Alimentary Canal. 



1. The pharynx is an ovoid muscular mass immediately 



behind the mouth. 



2. The oesophagus is a very short straight thin-walled tube' 



behind the pharynx. 



3. The intestine, into which the oesophagus opens just in 



front of the genital aperture, divides immediately 

 into a right and a left limb, each of which runs to 

 the hinder end of the body, giving off numerous 

 small csBca on its inner side, and many large branched 

 ones on its outer side ; the whole intestine forming 

 a series of csecal tubes ramifying all over the body 

 without anastomoses. 



C. The Excretory System. 



This is usually invisible except in injected specimens. It 

 consists of a network of minute and much-branched ducts, 

 which commence with slightly dilated ends into which project 

 long ilame-shaped cilia. The small ducts freely anastomose 

 with one another, and open into larger transverse ducts, which 

 in turn open into the main duct. 



The main duct is a medium tube of considerable size, 

 formed by the union of four anterior ducts, a dorsal and a 

 ventral on each side, at about a quarter of the animal's length 

 from the anterior end : from this point the main duct runs 

 directly backwards to open to the exterior by a terminal, 

 median pore. 



D. The Reproductive System. 



This is complicated, as in most hermaphrodite animals. 

 1. The male organs. 



a. The testes are much-branched tubes, lying in the 

 middle part of the body, and extending over 

 about half its length and half its width. The two 

 testes are about equal in extent, one lying behind 

 the other. 



