44 ILLINOIS BIOLOGICAL MONOGRAPHS [490 



forward and two backward soon to become lost in the body wall. Very 

 few observations on the nervous system of the redia are found in the 

 literature. Looss (1896:199) traced the nervous system of the redia of 

 Cercaria distomatosa about as far as it is followed in the above descrip- 

 tion. He speaks of this as the best developed of the nervous systems 

 described in the redia up to that time. The degree of development of 

 the nervous system as he suggests is correlated with the degree of 

 mobility of the redia. 



In the largest of the rediae (Fig. 45) almost all the germ balls 

 have developed into mature cercariae, of which from twenty to thirty are 

 present. The body cavity is much enlarged, the cercariae having pushed 

 clear into the posterior tip, into the posterior locomotor appendages 

 and up around the oral sucker. The rediae are mere shells, the anterior 

 collar having been obliterated and the posterior locomotor appendages 

 much reduced. The length of one of the largest rediae found was 2.26 

 mm., the width 0.30 mm. and the posterior locomotor appendages were 

 1.65 mm. from the anterior end. The oral sucker is very little different 

 in size from that in the younger specimens, its diameter being 0.056 

 mm. The intestine was long and slender and reached to a point 1.15 

 mm. from the anterior end. 



That Cercaria reflexae is closely related to the echinostomes is shown 

 by a comparison with Cercaria trivolvis. The rediae of the two species 

 have much the same general structure. In fact it would be practically 

 impossible to distinguish between very young rediae of the two forms. 

 Further, the locomotion and general body structures of the two cercariae 

 are similar. The arrangement of the anlage of the reproductive organs 

 of the two forms is much* alike. That Cercaria reflexae is simply an 

 immature echinostome cercaria in which the crown of spines has not 

 developed is improbable from the fact that its other structures are 

 those of a well advanced cercaria, the anlagen of the reproductive 

 organs especially being considerably differentiated. No record has been 

 found of any species either cercaria or adult which agrees with Cercaria 

 reflexae. 



MICROCERCOUS CERCARIAE 



Among thirty-six specimens of Campeloma subsolidum from Hart- 

 ford, Connecticut, four were found to be infected with rediae and very 

 short tailed cercariae. The infection was in the tissues of the body 

 above and at the bases of the gills. This form, which has a very short 

 triangular tail, I propose to name Cercaria trigonura. 



The cercariae were free in the tissues of the snail, were numerous, 

 and were all in the same stage of development. When freed, they ex- 



