PARASITIC FLATWORMS 417 



204 (210) Caudal pocket present, distinct, devoid of hooks or spines. . 205 



205 (206, 207) Ceca short, lateral trunks of excretory bladder circumscribe 

 acetabulum C. brevicaeca Cort 1914. 



Body elongate oval, 0.3 mm. long, 0.14 mm. wide. Tail caducous, 

 slender in length about equal to body. Oral sucker 0.082 mm., ace- 

 tabulum 0.087 mm. in diameter. Stylet glands 10 to 12 on each side. 

 Intestinal ceca short. Anterior half of body spinous. A poor swim- 

 mer. 



Found in sausage-shaped sporocysts in liver of Physa anatina 

 from Manhattan, Kansas. 



FIG. 720. Cercaria brevicaeca; a, free hand drawing, ventral view. Cys- 

 togenous glands not shown. X about 100. b, stylet, ventral view. X 290. 



206 (205, 207) Ceca arise directly from pharynx region, excretory bladder 



muscular, crenate, capable of great distension. 



Cercaria crenata Faust. 



Body length 0.25 mm., width 0.13 mm. Tail weak, 0.15 to 0.16 mm. in length, 0.02 to 0.03 

 mm. wide at base. Body oblong-ovate, with deep pocket at posterior extremity for reception 

 of tail. Stylet glands 13, 8 in outer series and 5 in inner series, minute, extending to mid- 

 acetabular region. Esophagus lacking. Sporocysts small oblong-ovate. In liver tissue of 

 Lymnaea proximo Lea from springs at Fort Missoula, Montana. 



207 (205, 206) Ceca undeveloped, excretory bladder bicornuate. . . . 208 



Cort regards these forms as a natural group characterized by development in elongate sac- 

 shaped sporocysts in Gastropoda, with a slender tail, not usually shorter than the body, with 

 a small post-central acetabulum, a stylet 30 /JL long, with six or more stylet glands on each 

 side in front of acetabulum, and a bicornuate excretory bladder. He considers that they prob- 

 ably belong to the Plagiorchiinae. Nothing is known regarding the development of the 

 American species. 



208 (209) Six stylet glands on each side. 



Cercaria isocotylea Cort 1914. 



Develops in sporocysts. Tail small, very extensile. Suckers rela- 

 tively large. Stylet glands just in front of ventral sucker. Excretory 

 pore dorsal, at base of tail. Genital glands indicated by nuclear mass 

 dorsal and anterior to acetabulum, and a larger mass dorsal and pos- 

 terior, but connected with the former by a band on left margin of ace- 

 tabulum. 



From Planorbis trivolvis at Urbana, Illinois. 



FIG. 721. Cercaria isocotylea; a, ventral view. X 207. b, stylet, ventral and 

 side view. X 290. (After Cort.) 



