164 



PLATHELMINTHES 



GYEATRIX Ehrenberg. With the characters of the family : 2 species. 



G. hermaphroditus Ehr. Body 2 mm. long and very contractile, 



transparent: in fresh and salt water; eastern states; Europe; very common. 



SUBORDER 2. ALLCEOCCELA. 



Fresh-water and marine turbellarians in which the intestine is an 

 irregular sac or tube often with lateral diverticula; 1 or 2 genital pores 

 present; testes and ovaries consist of numerous 

 follicles: 7 families with about 75 species, 30 

 American. 



FAMILY PLAGIOSTOMIDAE. 



Intestine sac-shaped and without lateral diver- 

 ticula; pharynx variable and in forward part 

 of the body ; genital pore single 

 and in hinder third of body; 

 ovary and yolk glands distinct : 

 30 species, 10 American. 



PLAGIOSTOMUM Schmidt. 

 Two or 4 eyes present ; pharynx 

 large, sac-shaped : 10 American 

 species; marine. 



P. wilsoni von Graff (Fig. 

 262). Length 1.5 mm.: com- 

 mon at Woods Hole. 



Fig. 262 

 Plagiostomum 



wilsoni 

 (von Graff). 



1, mouth 



2, intestine 



3, genital pore. 



Fig. 263 Diagram of 

 trie 



clad (von Graff). 

 1, brain ; 2, ovary ; 3, 

 yolk gland ; 4, testis ; 

 5, intestine ; 6, phar- 

 ynx ; 7, mouth ; 8, 

 penis ; 9, genital pore ; 

 10, vagina ; 11, uterus. 



ORDER 2. TRICLADIDA. 



(Fio. 263.) 



Marine, fresh-water, and 

 terrestrial turbellarians in which 

 the intestine is composed of 3 



main trunks with many branches, one trunk extending forwards from the 

 pharynx, and the other two backwards ; body flattened, with sensitive lobes, 

 projections or tentacles and a pair of eyes 'at or near the forward end, 

 and in certain species a ventrally situated sucker; mouth and genital pore 

 in or behind the middle of the body; proboscis well developed: about 430 

 species and 6 families grouped in 3 suborders. 

 Key to the suborders of Tricladida: 



a^ Aquatic triclads. 



&! Fresh-water triclads ; planarians 1. PALUDICOLA 



6 2 Marine triclads 2. MABICOLA 



2 Terrestrial triclads. 3. TERBICOLA 



