PARASITIC FLATWORMS 441 



65 (70) Rostellum hassock-shaped with a multitude of very small hooks 



arranged in a double row. 



Family Davaineidae Fuhrmann 1907 . 66 



Scolex with rostellum usually broader than high and armed with very many minute hammer- 

 shaped hooks. Margins of suckers usually with small hooks. Genital organs usually single, 

 rarely double in each proglottid. Testes numerous. Onchosphere with two thin membranes. 



66 (67) Uterus divides into numerous separate parenchyme-capsules. 



Davainea R. Blanchard 1891. 



Rostellum armed with double row of hooks; dorsal excretory vessels present. Reproductive 

 organs single in each proglottid. Genital pores unilateral or occasionally irregularly alternate. 

 Uterus breaks down into egg capsules each containing one or several eggs. Adults in mam- 

 mals and birds. Numerous species; mostly in scratching birds. D. anatina is reported from 

 the domestic duck in Europe. No North American records. 



67 (66) Uterus not breaking up into separate parenchyme-capsules. . . 68 



68 (69) No parauterine organ; uterus sac-shaped. Rostellum broader than 



scolex with several thousand booklets. 

 Ophryocotyle Friis 1870. 



Rostellum broader than rest of scolex; suckers 

 armed only near anterior border. Reproductive or- 

 gans single in each proglottid. Uterus sac-Uke, per- 

 sistent. 



Three species in European shore and water birds 

 some of which occur in North America. 



Fig. 745. Ophryocotyle proteus. Head and neck with 

 retracted and extended infundibulum; magnified. (After 

 Stiles.) 



69 (68) Uterus coiled in posterior end of proglottid; thick-walled para- 



uterine organ in anterior region. Rostellum small; with 

 not to exceed a few hundred booklets. 



Idiogenes Krabbe 1868. 



Small cestodes. Genital pores unilateral. Cirrus-pouch very large, with retractor. Para- 

 uterine organ develops in front of uterus; eggs finally pass directly into it from uterus and it 

 is transformed into single thick-walled egg capsule. Adults m birds. 



A few species in water birds; none recorded as yet in North America. 



70 (65) Rostellum sac-like, or lacking. . . . 71 



71 (82) Not more than four testes in each proglottid. 



Family Hymenolepididae Fuhrmann 1907. . 72 



Scolex armed with 8 to 40, usually 10 hooks, with points directed posteriad when at rest, 

 on a more or less elongated rostellum which rarely is rudimentary and unarmed. Genital 

 pores strictly unilateral in entire strobila. Genital ducts dorsal to excretory ducts and longi- 

 tudinal nerve. Female glands median. Onchosphere with three membranes. Adults in 

 birds and mammals. 



72 (73) In each proglottid normally 4 testes. Oligorchis Fuhrmann 1906. 

 A single species in North America; not reported in aquatic birds. 



73 (72) In each proglottid normally less than four testes 74 



74 (79) In each proglottid normally three testes 75 



