41 8 FRESH-WATER BIOLOGY 



209 (208) Twelve stylet glands on each side. Cercaria polyadena Cort 1914. 



Encysts readily. Tail active, easily detached, somewhat larger than 

 in last species. Oral suclter smaller, stylet glands more numerous. Body 

 also larger than former species. Genital system marked out by S-shaped 

 nuclear mass, elongate and dorsal to acetabulum. 



1*10.722. Cercaria polyadena; a, ventral view. Cystogenous glands not shown. 

 X 207. b, stylet, ventral view. X 290. (After Cort.) 



210 (204) Caudal pocket distinct, provided with hooks or spines that are 



mostly situated in postero-lateral sacs. . . . 211 



211 (212) Digestive tract naked, ceca rudirhentary. 



Cercaria dendritica Faust. 



Body length 0.38 to 0.40 mm., width 0.16 to 0.17 mm. Tail small, 0.16 mm. in length, 

 0.04 mm. wide at base. Body obovate, muscular; cuticula thick. Caudal pocket lined with 

 spines. Excretory bladder large, muscular, bicomuate; tubules dendritic. In long oval sporo- 

 cysts in liver of Lymnaea proxima Lea, sloughs of Bitter Root River, Fort Missoula, Montana. 



212 (211) Digestive tract provided with special glands, in addition to stylet 



glands. Ceca developed 213 



213 (214) Glands along entire course of digestive tract. Three median 



spines on lip of caudal pocket. . Cercaria glandulosa Faust. 



Body length 0.45 mm., width 0.2 mm. Tail length 0.35 mm. by 0.05 to 0.06 mm. at base. 

 Body oblong-ovate, acetabulum sHghtly behind center of body, smaller than oral sucker. 

 Esophagus long, ceca short, unicellular glands along entire digestive system. Cuticula delicate. 

 Eight cephalic glands. Body filled with cystogenous glands. In sporocysts, in Uver of Physd 

 gyrina Say, Bitter Root River, Corvallis, Montana. 



214 (213) Glands in pharynx region only, spines confined to pockets of 



caudal pocket. . .... . . 215 



215 (216) Ceca attenuate, excretory bladder with long median shank. 



Cercaria diaphana Faust. 



Body oblong-ovate to ovate. Acetabulum median, about half size of oral sucker. Pharynx 

 small, surrounded by great mass of unicellular glands. Cephahc glands 8, anterior to cecal 

 bifurcation. Stylet set with an internal spine at anterior end. Body length 0.2 to 0.26 nmi., 

 width o.io to 0.12 mm. Tail 0.15 mm. in length by 0.04 mm. wide at base. In oblong 

 sporocysts in liver tissue of Lymnaea proxima Lea, Bitter Root River, Corvallis, Montana. 



216 (215) Ceca inflated, excretory bladder bicomuate, inflated. 



Cercaria micropharynx Faust. 



Body minute, ovate, covered with fine spines. Acetabulum mid-ventral, smaller than oral 

 sucker. Pharynx extremely small, esophagus short, ceca inflated. Digestive glands in pre- 

 pharynx region only. Body length 0.18 mm., width 0.09 mm. Tail 0.14 mm. in length by 

 0.03 mm. at base. In oval sporocysts with well-developed excretory tracts. Liver of Lymnaea 

 proximo Lea, Rattle Snake Creek, Missoula, Montana. 



217 (201) Tail modified, not of simple form 218 



