188 



PLATHELMINTHES 



jection situated just back of the acetabulum; body in most cases made 

 up of 2 distinct regions, a wider anterior portion containing the 2 

 suckers and the disc, the lateral edges of which are often rolled in 

 ventrally and medially, and a posterior portion containing the genital 

 organs; the genital openings being at the hinder end in a deep depres- 

 sion called the bursa copulatrix; the arrangement of the internal organs 

 is similar to that of the Distomata: in the intestine of vertebrates, princi- 

 pally mammals and birds; about 6 genera and 60 species. 

 Key to the genera of Holostomata here described : 



Oi Lateral edges of anterior portion not rolled in medially 1. Diplostomum 



Oj Edges of anterior portion rolled in. 



6i Anterior portion trough-shaped 2. Hemistomum 



6, Edges of anterior portion fused midventrally 3. Stkigea 



1. Diplostomum Nordmann. Body composed of 2 distinct portions ; 

 a large sucking disc back of the acetabulum: in the intestine of the 

 Crocodilia and of birds; intermediate hosts, fish; about 15 species. 



D. grande Diesing. Oral sucker and acetabulum small; sucking 

 disc at the bottom of a deep cavity, the opening of which is on a conical 



projection just back of the acetabulum; 

 length 4 mm.: in the intestine of the 

 snowy owl. 



2. Hemistomum Diesing. Anterior 

 portion of body flattened, the lateral 

 edges being prolonged medially, forming 

 a trough; behind the acetabulum and 

 sometimes projecting over it is an elon- 

 gated adhesive elevation: in the liver of 

 birds and mammals; about 15 species. 



H. alatum (Goeze) (Fig. 309). 

 Length 6 mm.; acetabulum smaller than 

 the oral sucker, at each side of which 

 is a crescent-shaped opening of glands: 

 in the stomach and intestine of the fox 

 and dog. 



3. Strigea Abildgaard (Holostomum Hudolphi). Lateral edges of 

 the forward portion of the body prolonged medially and joined mid- 

 ventrally, making this part of the body cup-shaped; behind the acetabu- 

 lum is a conical adhesive elevation in a deep cavity: in the intestine of 

 birds, rarely in fish and amphibians; about 30 species. 



S. variegata (Dujardin) (Fig. 310). Conical elevation usually pro- 

 jecting from the cup; length 6 mm.; testes branched; genital bursa at 

 hinder end: in gulls, grebes, and loons. 



Fig. 309 



Fig. 310 



Fig. 309 — Hemistomum alatum 

 (Braudes). a, adhesion elevatiou. 

 Other references as in Fig. 293. 

 Fig. 310 — Stricjea variegata (Bran- 

 des). a, adhesion elevation; m, 

 mouth ; b, genital bursa ; c, cup- 

 shaped anterior end. 



