382 



FRESH-WATER BIOLOGY 



37 (48) No ventral sucker present; oral sucker only adhesive organ present. 



Suborder Monostomata Zeder . . 38 



Endoparasitic trematodes with flattened body and single sucker which surrounds mouth 

 at anterior end. Intestinal crura often unite in posterior end of body. Genital pore usually 

 ventral or marginal in anterior region, or rarely rnedian posterior. Life history relatively un- 

 known. For developmental stages see 174 (183) in this key. 



Forms not well known, though frequent especially in reptiles (turtles) and birds; rarely also 

 mammals. North American records scanty. 



Most of the forms described from this continent as " :Monostomum " cannot be located 

 except generally in this section since the data are lacking on which a more exact determina- 

 tion depends. It is indeed likely that some of them were wrongly placed in this group and 

 more complete knowledge of their structure will result in their transfer to some other section. 

 Until the specimens are restudied they must all be regarded as uncertain. Such doubtful 

 forms are those hsted as Monostoma sp. in Stiles and Hassall's Catalog (1904) and the following: 



Monostoma affine Leidy from muskrat, M. aminri Stafford from bullhead, M. aspersnm 

 Vaill of Pratt from salamander, M. incommodum Leidy from alligator (which later the author 

 conjectured to be in fact a distome), M. ornatum Leidy from frog, M. spatulatum Leidy from 

 "fish." 



Odhner contends that the monostomes are isolated members of other groups that have 

 lost all suckers save the oral and that they should be classed in the various families from which 

 they have sprung. For practical reasons it will be necessary to retain the group at least until 

 its forms are much better known. 



38 (45) With two compact testes, and follicular vitellaria 39 



39 (44) Body elongated. Not parasitic in dermal cysts 40 



40 (41) Intestinal crura connected at posterior end. Testes near posterior 



end, within crura, asymmetrical. Ovary between testes, 

 and intercecal but opposite to them. 



Family Cyclocoelidae Kossack 1911. 



Large monostomes with thick, muscular body, somewhat flattened. Esophagus short, no 

 pharynx. (Kossack designates the structure which lies near the mouth as the pharynx; I have 

 called it the oral sucker. He says these forms do not possess an oral sucker.) Intestinal 

 branches simple or with small ceca on the inner side connected at posterior 

 end by continuous arch. Genital pore median, ventral to and near oral 

 sucker. Receptaculum seminis and Laurer's canal wanting. Vitellaria well 

 developed, lateral and sometimes dorsal to intestine; transverse duct just in 

 front of posterior testis. Uterine coils numerous, regular, transverse, occu- 

 pying space between posterior testis and fork of intestine. Eggs numerous, 

 without polar filaments. 



Air passages of water birds; frequently reported as in body cavity. 



Only American genus. . . . Cyclocoelum Brandes 1892. 



Intestinal crura simple, genital pore near sucker, or at anterior margin. 

 Cirrus sac small, rarely extending beyond fork of intestine. Vitellaria 

 extracecal from fork of intestine to posterior end, not continuous with 

 opposite side. Reproductive glands in posterior region in arch of intestine 

 at corners of triangle. Ovary smaller than testes, on side opposite them. 

 Uterine coils do not extend laterad beyond the intestinal branches. Eggs 

 thick-shelled, large. 



The species designated by Leidy as "probably Monostoma mutabile 

 Zeder" belongs here if his determination be accepted. It was collected 

 from the gray snipe {Gallinago wilscni). 



Fig. 664. Cyclocoelum mutabile. X 3- (After Kossack.) 



41 (40) Intestinal crura end blindly at posterior end. Testes symmetrical, in 

 posterior region, outside of crura. Ovary intercecal, between 

 testes. . . . Family Notocotylidae Liihe 1909 . . 42 



Small monostomes with elongated flattened body tapering and rounded at both ends. On 

 ventral surface several (3 to 5) rows of small excrescences or papillae with unicellular dermal 

 glands Esophagus short, no pharynx; intestinal ceca simple, long, not united in posterior 



