PARASITIC FLATWORMS 



385 



47 (46) Vitellaria extend from ovary to posterior end of body. Seminal 

 receptacle absent. . . . Aorchis Barker and Parsons 1914. 



Oral sucker small, weak, pharynx large, esophagus short, 

 intestinal ceca long, not united at posterior end. Ovary entire, 

 just behind fork of intestine. Vitellaria compact, tubular, 

 coarsely lobed or with short irregular branches extending almost 

 entire length of body. Two divisions of uterus looped or coiled 

 around intestinal ceca. Other two divisions straight longitudi- 

 nal tubes. Terminal division conspicuous, heavy, dark band 

 through length of the body in the median plane. Testes 

 elongate, tubular, irregularly lobed. Genital pore ventral, 

 near anterior tip of body. Eggs with short polar stalk at one 

 end. 



Type species. 



Aorchis extensus Barker and Parsons 1914. 



Lungs of Chrysemys marginata, Mississippi River (Minnesota) 

 and also, in various turtles from Michigan, Indiana, Illinois, 

 Nebraska. 



FIG. 669. Aorchis extensus. Only anterior portion of testes shown 

 in drawing. X 8. a, Embryos in uterus; note conspicuous eye spots. 

 X 22. (Original.) 



48 (37) Ventral sucker present, usually single though varied in form and 



position; never represented by numerous small organs in 

 series 49 



The acetabulum or ventral sucker proper is a closed organ, not possessing any inner opening 

 or connecting with any special organ or system. It may be so insignificant hi size as to be 

 difficult to 'distinguish, in which case the form is erroneously diagnosed as a monostome as has 

 often occurred. On the other hand it may be as wide as the body or wider and so powerful 

 as to distort the form of the animal. It may be sessile or be borne on a stalk or peduncle. 



In some species a special secondary sucking organ is developed around the genital orifice 

 and this may even become so highly differentiated as to exceed in size or include the true ven- 

 tral sucker. Those forms which possess this highly developed adhesive organ ordinarily have 

 the body divided into two distinct regions. 



In location the acetabulum is near the posterior end in the group of amphistomes and at or 

 anterior to the center of the body in the distomes and holostomes. The latter are readily 

 recognized by the peculiar adhesive organ and the separate regions of the body even though 

 the details of form are very variable in different genera. 



49 (62) Acetabulum terminal or subterminal and posterior to the repro- 



ductive glands Suborder Amphistomata Nitzsch. 



Endoparasitic trematodes with oral opening anterior and terminal. Oral sucker powerful, 

 oval or more elongate, often with two dorso-lateral muscular pockets. Acetabulum conspicu- 

 ous, much larger than oral sucker, at "or very near posterior end. Body muscular, thick, little 

 flattened and often conical, tapering anteriad. Skin without spines but regularly provided 

 with sensory or glandular papillae. Excretory bladder sacculate, with median ventral pore 

 near posterior end. Genital pore ventral, median, in anterior region. Testes large anterior 

 to small ovary. Vitellaria follicular, lateral, paired. Uterus simple, with few coils. Eggs 

 numerous, small, plain. Development complex with alternation of generations and hosts. 



Only family recognized. 



PARAMPHISTOMEDAE Fischoeder 1901 . . 50 



50 (61) Oral sucker terminal; acetabulum simple, not divided 51 



51 (52) No postero-lateral pockets on pharynx. 



Subfamily PARAMPHISTOMINAE Fischoeder 1901. 



None of these forms is parasitic as adults in aquatic animals. One species occurs in domes- 

 tic ruminants in North America. The redia and cercaria develop in some freshj water snails as 

 is known of the related European forms. Compare 185 in this key. 



