501] LARVAL TREMATODES—CORT 55 



were found in the liver with the rediae of Cercaria reflexae. These 

 sporocysts were much like those of Cercaria isocotylea, and were 

 so thin walled and so closely interwoven with the lobes of the liver that 

 none were isolated for accurate measurements. Altho large numbers 

 of the cercariae in the sporocysts were mature, few were free in the liver 

 of the host. When, however, the liver was taken out of the snail many 

 were freed and swam actively about. I propose the name Cercaria poly- 

 adena for this species from the fact that the body of the cercaria contains 

 such large numbers of gland cells. 



The position of Cercaria polyadena in swimming was similar to that 

 of Cercaria isocotylea. The tail was, however, somewhat stronger than 

 in the latter species and the animal was able to move forward definitely 

 and fairly rapidly. Whenever the cercaria came in contact with a sur- 

 face, it immediately settled down, took hold with its suckers, and crept 

 along. 



The tail was very easily detached from the body and would con- 

 tinue swimming for some time with a wriggling motion. Whenever an 

 actively detached tail came in contact with the substratum, it ceased 

 wriggling and alternately extended and contracted as if it were still 

 attached to a living cercaria. One of the detached tails kept up active 

 movement for over fifteen minutes and then was stopped by the drying 

 up of the water around it. 



Small thin walled cyst containing tailless individuals of Cercaria 

 polyadena were found scattered in with the material preserved for study 

 (Fig. 71). It is probable that these cysts were formed after the liver 

 was removed from the snail, and that Lymnaea reflexa is not the sec- 

 ondary intermediate host of this species. The formation of the cyst 

 was not observed but that the glands were ready for secretion is shown 

 by the fact that the extrusion of the cystogenous material was observed 

 in one individual that was flattened under a cover slip. The cysts 

 were round and varied in diameter from 0.15 mm. to 0.16 mm., and 

 the transparent cyst wall varied in thickness from 0.005 to 0.007 mm. 



Cercaria polyadena (Fig. 70) is very variable in shape, living speci- 

 mens changing from 0.12 mm. when contracted to 0.30 mm. at greatest 

 extension. When most contracted the tail may be less than one-half 

 the body length, but when the animal was swimming it reaches to 

 0.30 mm. The average measurements of five mounted individuals in 

 about the state of contraction of the figure, give the length of 0.18 

 mm., the width of 0.07 mm., the length of the tail 0.12 mm. and its 

 width 0.017 mm. The tail is attached in a groove on the ventral sur- 

 face of the posterior end, and altho it is small for the size of the body 

 it is relatively larger than in Cercaria isocotylea. 



