50 INTESTINAL TREMATODES 



B. Systematic Position of Human Forms 



All human trematodes belong to the sub-class Digenea, 

 which are endoparasitic, have an alternation of generations 

 and a molluscan intermediate host. Two of the human 

 trematodes Gastrodiscoides hominis (Gastrodiscus hominis) 

 and Watsonius watsoni belong to the group Amphistomata, 

 which is characterised by the presence of a large acetabulum 

 at the posterior end. All of the other human trematodes 

 belong to the group Distomata, in which the acetabulum 

 is ventral and separated from the posterior end by all or 

 part of the reproductive system. The human trematodes 

 will be considered according to their position in the human 

 host. 



C. Intestinal Trematodes 



Until recently but little has been known in regard to the 

 intestinal trematodes of man. The two amphistomes, 

 Gastrodiscoides (Gastrodiscus) hominis and Watsonius 

 watsoni, have been reported only a few times from man, 

 the former from Africa and the latter from Assam and India. 

 Their structure has been carefully worked out, but nothing 

 is known of their life histories and method of entrance into 

 man. Three echinostomes, i.e., distomes with a circumoral 

 ring of prominent spines, have also been reported from the 

 intestine of man. Of these species Echinostoma ilocanum 

 was found in the Philippine 'Islands, Euparyphium malay- 

 anum (Echinostoma malayanum) in the Malay States and 

 Artyfechinostomum sufrartyfex in India. These last two 

 forms may belong to the same species. Three other intes- 

 tinal flukes of man Fasciolopsis buskii, Heterophyes hetero- 

 phyes and Metagonimus yokogawai are of sufficient impor- 

 tance to require further description. 



