30 ILLINOIS BIOLOGICAL MONOGRAPHS [476 



shows how fundamental are the differences between the cercariae used in 

 the experiments and Diplodiscus temporatus. 



The second experiment is even less convincing than the first because 

 no check whatever is given and the source of the tadpoles is not indi- 

 cated, altho it is perhaps to be taken for granted that they are obtained 

 from the same source as the first batch. These tadpoles were killed each 

 week to note the development of the parasites and stages of Diplodiscus 

 temporatus were found. If the development had followed the course 

 that the writer maintains it would have been possible with this material 

 to find transitional stages in change of shape, supposed migration of the 

 acetabulum, etc. This Cary has not done and even the possibility seems 

 to have escaped his notice, since it is not mentioned in the paper. 



The following points have been proved in the above discussion. 



1. That Cary described two entirely different species of cercariae 

 as belonging to Diplodiscus temporatus; 



a. Those with stylets, which develop in sporocysts, 



b. Larger forms without stylets which develop in rediae. 



2. That since the second type only were used in the infection ex- 

 periments, no connection between the first type and Diplodiscus tem- 

 poratus can have been shown. 



3. That the infection experiments were not sufficiently controlled 

 to be conclusive. 



4. That the cercariae used could not have possibly developed into 

 Diplodiscus temporatus, since the two forms differ so fundamentally in 

 structure. 



Since the stylet form of Cary's two species, which I have named 

 Cercaria caryi, is very small, and no living material is available, it does 

 not seem wise at the present time to attempt a detailed description. 

 Figure 26 gives the most salient features. From the presence of the 

 Stylet, the small number of the stylet glands, and the small size of the 

 acetabulum it may be placed with the Xiphidiocercariae in Liihe's group 

 of the Cercariae microcotylae (Liihe, 1909: 196-198). 



I was fortunate enough to obtain further material of the larger 

 form, so that a detailed description of it is possible. On account of the 

 great length to which the tail is sometimes stretched I shall describe it 

 as Cercaria megalura. 



