PLATYHELMINTHES 



157 



Most of the Trematoda are hermaphroditic. At maturity the sexual 

 organs reach a high degree of development adaptive to the mode of 

 parasitism (Introduction, p. 5). The male sexual organs consist of 

 tube-like testes, from which spermatic ducts take origin. These unite 

 in a large seminal vesicle, the terminal portion of 

 which is usually inclosed in a pouch. The ovary 

 is also branching and tube-hke. With the oviduct 

 there unite ducts from the vitellaria or yolk-glands, 

 this union being followed by the much convoluted 

 uterus which receives the eggs and terminates by 

 the side of the male sexual opening (Fig. 86). 



The entoparasitic trematodes undergo a compli- 

 cated life history, involving alternation of hosts 

 and, within the intermediate host, multiplicative 

 generations. A typical example of this cycle is 

 given further on in reference to the species Fasciola 

 hepatica. 



Most of the trematode parasites of mammals 

 live in the liver, producing the affection known as 

 hepatic fascioliasis (distomiasis), or commonly as 

 liver rot. Others invade the blood, lungs, and 

 stomach, causing, accordingly, vascular, pulmonary, 

 and gastric fascioliasis. The latter forms are rarely 

 met with in the United States. 



The species to be considered come under three 

 families, as follows: 



Family I. Fasciolidse. — The conamon liver flukes. 



Family II. Amphistomidae. — Of the rumen. 



Family III. Schistosomidse. — The blood fluke. 



Fig. 85.— Sketch of 

 Fasciola hepatica, 

 showing bifurcated and 

 branching alimentary 

 tract: si, mouth and 

 anterior sucker; s2, 

 posterior sucker; t. a., 

 alimentary tract, — en- 

 larged (after Boas, by 

 Kirkaldy and Pollard, 

 from Thomas). 



Classification of Parasites of the Phylum Platyhelminthes 



Phylum II. Platyhelminthes. P. 155. 

 Class A. Trematoda. Flukes. P. 156. 

 Order 1. Distomese. P. 156. 

 Family (a) Fasciohdse. P. 160. 

 Genus and Species: 

 Fasciola hepatica. Hosts, sheep, cattle, etc. P. 160. 

 Dicroccelium lanceatum. Hosts, same. P. 160. 

 Fasciola americanus. Hosts, same. P. 160. 

 Family (b) Schistosomidse. P. 168. 

 Genus and Species: 



Schistosoma bovis. Hosts, cattle, sheep. P. 168. 

 Family (c) Amphistomidae. P. 167. 



