422 



FRESH-WATER BIOLOGY 



238 (239) Distome fills three-fifths of stem of anchor. 



Cercaria wrightii Ward 1916. 



Length 0.75 mm., width 0.133 mm. Flukes measure 0.53 by o.i mm. Young distome 

 0.45 by o.i mm. Genital rudiment forms rod-like mass partly preacetabular and partly 

 postacetabular. 



Originally described as a free-swimming sporocyst by R. R. Wright, it was shown by obser- 

 vations of Braun on the European C. miriabilis to be a highly modified cercaria. Found 

 in an aquarium at Toronto. 



239 (238) Distome fills less than half of stem of anchor. 



Cercaria anchor aides Ward 1916. 



Length 2 mm.,' width 0.24 to 0.34 mm.; flukes 

 curved, tips 0.84 mm. apart. Young distome 0.64 

 by 0.288 mm. Germ glands already laid down in 

 middle third of body. Ovary postacetabular, pre- 

 testicular; testes oblique. Genital pore preacetabu- 

 lar. Adult unknown. 



FIG. 727. Cercaria anchoroides. Young distome just set 

 free. X 73- Cercaria complete. X 27. (Original.) j 



240 (235) Tail of cercaria does not envelop young distome, but is modified 



in form 241 



241 (246) Modification consists in forked end. 



Furcocercous cercariae . . 242 



The long slender tail is split in its distal region and terminates in two slender branches, 

 one-third to one-half the length of the entire structure. An unnatural group as this modi- 

 fication has apparently arisen more than once in different types. 



242 (243) Cephalic glands with short ducts, never reaching acetabulum. 



Cercaria douthitti Cort 1914. 



Develops in sporocysts. Tail bifid; nearly twice as long as body. Oral 

 sucker very large. Two pigment eye-spots with lenses. Eight large cephalic 

 glands in posterior region with ducts opening into or through oral suckers; 

 no stylet found. Single genital nuclear mass at posterior extremity of body. 

 Found in Lymnaea reflexa from Chicago, 111. 



FIG. 728. Cercaria douthitti, ventral view. X 98. (After Cort.) 



