170 THE UNIVERSITY SCIENCE BULLETIN. 



ones exhibited a slightly waving motion. Under the cover slip 

 cercarise emerged from the redise, usually tail first, from the birth 

 pore near the anterior end. It required about two minutes for a 

 cercaria to free itself from the redia. This form did not encyst, 

 but the cercarise soon died in the water, in no case living more 

 than four hours after emerging from the snail. Those liberated 

 when the snail was crushed lived only from eight to twelve min- 

 utes. The number of this species emerging from a single snail 

 was estimated at five thousand, 



Cercaria inversa is a small furcocercous form, corresponding as 

 to size, shape and behavior to Cercaria douthitti described by Cort 

 (1915), from Lymnaea reflexa. This species, however, contains no 

 eyespots and is found in rediae instead of sporocysts. The length 

 of the body is .16 mm. in well-extended specimens, and the width 

 is .045 mm. The unbranched part of the tail has a length of .26 

 mm. and a width of .027 mm., while the lobes are five-sixths as 

 long as the main part of the tail and one-half as wide. These 

 lobes taper to rather a sharp point. The openings in the suckers 

 are about the same size, .01 mm., but the outside dimensions 

 of the oral sucker are greater than those of the ventral sucker. 

 The measurements are, oral sucker .042 mm. and ventral sucker 

 .028 mm. 



As in Cercaria douthitti, the region back of the center is filled 

 with large cephalic glands. The ducts of these glands extend 

 forward and open alongside the oral sucker (fig. 50). The excre- 

 tory system of the body region could not be traced, but a duct 

 extends through the main part of the tail and is joined by ducts 

 from each branch. An excretory pore opens to the exterior be- 

 tween the forks of the tail. 



The anlage of the reproductive organs is a mass of small cells 

 near the posterior end of the body and ventral in position. 



Six per cent of large numbers of Physa gyrina collected at Lake- 

 view, Kan., August 20, were infected with a form for which I pro- 

 pose the name Cercaria echinocauda. Collections of snails from 

 the same locality, made October 12, showed two per cent to be 

 infected. 



This cercaria was very active, swimming both foi'wards and 

 backwards, but usually forwards, with a vibratile motion of the 

 tail. The tail was loosely attached to the body and was easily 

 severed. When this occurred the body died in about twenty 

 minutes, while the tail lived for two hours, swimming about 



