RESEARCHES IN HEEMINTHOLOGY AND PARASITOLOGY. I45 



Cercaria, white, witli an obcordate or when elongated a clavate 

 body, and a long, narrow, cylindro-conical pointed tail. Cephalic 

 end triangular, and slightly constricted from the rest of the body ; 

 posterior part broadly emarginate. A ventral acetabulum near or 

 posterior to the center of the body, and between it and the root of 

 the tail an oval pore. Eyes none. Pharynx globular ; gizzard 

 small ; divisions of the intestine extending about two-thirds the 

 length of the body. 



Length of sporocysts of different ages, from i-Sth to i mm. 

 Length of cercarise i-4th to 2-5ths mm. 



In motion the sporocysts contract the head so that it may be of 

 nearly equal length and breadth, and it may be extended so as to 

 be double the length of the breadth. The body also elongates and 

 shortens in the same manner. Cercarise were observed in several 

 instances escaping from the snout-like projection of the body cavity 

 back of the head. The cercarise in movement elongate excessiveh', 

 and the body may be extended so as to be almost as narrow as the 

 root of the tail. The ventral disk is often protruded into a conical 

 appendage or expanded into a broad cup. The tail becoms longer, 

 narrower, and more pointed, or shorter, wider, and beaded. 



This fluke occupies a similar position in the Planorbis as in the 

 former, and has been found in equal numbers, but the two species 

 have not been found associated in the same individual. The distoma 

 form of the ascoid fluke, encysted, was also observed in Planorbis 

 parvus, without any traces of the generative organs being obvious. 



A free swimming cercariae, identical in character with that of the 

 ascoid fluke, has been ob-served in water, which contained many 

 individuals of Planorbis parvus and Limntsa elodes. The free cercaria 

 agrees with the description of Cercaria niinuta, Nitzsch, found with 

 various fresh-water mollusks of Europe. 



Prof. L. further exhibited drawings of a Disfoina, Xh.^ R/iopa/oa'rca 

 tardigrada, Diesing, from the rnanile oi Aiiodon ffuviati/is : a second, 

 the Heterostoniuni echinatum, Diesing, from the oviduct of Paludina 

 decisa, and a third from Helix aborea, thus described: 



Distoma Appendiculata. — Translucent white, band-like, widest in 

 front and rounded at the head, tapering behind and truncate at the 

 end. Pharynx and ventral disk large and nearly equal and about 

 I -8th mm. diameter. The gizzard comparatively large and oval. 

 Intestine bifurcate with the branches parallel, and with an inter- 

 mediate pouch-like appendage extending nearly half way to the 

 position of the ventral disk. A posterior opening communicating 



