PARASITIC FLATWORMS 



409 



156 (153) Ovary lateral and slightly posterior to anterior testis, but not 

 directly behind it 157 



157(158) Genital pore at posterior end. . . Leucochloridium Carus 1835. 



Small distomes with compressed muscular body. Both suckers and pharynx large and pow- 

 erful. Esophagus short, crura very slender, reaching nearly to posterior end. Excretory 

 pore dorsal near caudal tip. Cirrus sac present. Laurer's canal present; receptaculum 

 wanting. Vitellaria lateral, conspicuous, extracecal. Uterus in loops ascends on one side of 

 acetabulum, crosses body, and descends on the other side. Eggs small, thick shelled. 



In the cloaca of birds, not reported in North America. The larval stage in Succinea is a 

 sporocyst which sends into the tentacles of the snail branches that are banded in color and 

 are bitten off by birds. Reported in a personal letter by Mr. Bryant Walker who found it in 

 Succinea ovalis in Michigan. 



158 (157) Genital pore ventral, median, just anterior to posterior testis. 



Hasstilesia Hall 1916. 



Very small oval distomes, nearly round in cross section. Skin 

 with minute spines in anterior region. Suckers small, nearly 

 equal. Pharynx and esophagus present, equal in length; crura 

 irregular, reach to posterior end of body. Excretory bladder 

 minute with two delicate lateral branches. Genital pore ventral, 

 slightly dextral, midway from acetabulum to posterior end. Cir- 

 rus sac flask-shaped, large; cirrus long. Testes large, one in 

 extreme posterior region, nearly median, the other near center of 

 body on left. Ovary small, round, ventral to right intestinal 

 cecum, near anterior margin of posterior testis. Vitellaria lateral 

 in anterior half. Uterus in anterior region of body, moderately 

 developed, mostly pretesticular but with a single loop between 

 the testes. 



Eggs 13 by 20 IJL. 



Single American species. 



Hasstilesia tricolor (Stiles and Hassall) 1894. 



In small intestine of 'Lepus; abundant, Maryland, District of 

 Columbia, Virginia. 



FIG. 710. Hasstilesia tricolor. 

 Magnified. (After Stiles.) 



159 (64) Distomes of separate sexes. 



Family SCHISTOSOMATEDAE Looss 1899. 



Adults parasitic in blood vessels of man, cattle, and birds; not yet found in North America. 

 Cercariae very similar to those of this family occur in North American snails. 

 Compare furcocercous cercariae 241 (246) in this key. 



1 60 (63) Special adhesive organ behind acetabulum. Anterior region with 

 holdfast organs usually distinctly separated from posterior 

 region with genitalia Suborder Holostomata Liihe. 



The genus Cyathocotyle without differentiated regions has not been recorded in North 

 America. 



Only family represented. 



Family HEMISTOMIDAE Brandes 1888 , . 161 



Distomes with body more or less distinctly divided into two regions. Anterior region spoon 

 or cup-shaped, serving as adhesive organ. Suckers poorly developed, but with peculiar post- 

 acetabular sucking organ. Posterior region cylindrical or ovoid. Intestinal crura extend 

 to posterior end. Excretory bladder in form of subcutaneous network. Genital pore at 

 posterior end. Neither cirrus sac nor cirrus. Ovary and testes in series in posterior region. 

 Vitellaria conspicuously developed. Uterus short with few, very large, thin-shelled eggs. No 

 alternation of generations. Develop with intermediate host but without alternation of 

 generations. 



Parasitic in intestine of Amniota. 



