473] LARVAL TREMATODES—CORT 27 



When the adult Diplodiscus temporatus is compared with the larger 

 of the cereariae which Cary assigns to it certain differences of structure 

 are noted so fundamental that it seems impossible that the two forms 

 can be the same species. Compare figures 27 and 28. The adult is a 

 typical amphistome with the conical body terminating in a very large 

 acetabulum, while the cercaria is widest toward the anterior end, flat- 

 tened and its acetabulum which is only a little larger than the oral 

 sucker is just back of the center of the body. Certainly very remark- 

 able changes in shape and position of the organs would be necessary 

 before the cercaria which developed in rediae in Goniobasis virginica, 

 which Cary described, could metamorphose into an adult Diplodiscus 

 temporatus. Cary makes no attempt to bridge this gap altho it would 

 seem from his infection experiments that intermediate stages should have 

 been obtained. It is especially hard to believe that the ventral sucker 

 could have migrated from the middle of the body to the posterior 

 end and have become so much larger in proportion to the oral sucker, 

 and that the digestive system could have changed so fundamentaly 

 as would have been necessary. In those species of trematodes in which 

 the development is known the digestive and excretory systems are very 

 much alike in the cereariae and in the adults. The principal changes 

 come in the development of the reproductive organs and the correspond- 

 ing enlargement of body regions, usually the post-acetabular. 



The infection experiments that Cary conducted to prove the con- 

 nection between this cercaria and Diplodiscus temporatus seem con- 

 vincing until they are carefully analyzed. To carry conviction they 

 should have been better controlled, described in more detail and the 

 stages of development worked out. That I may do Cary no injustice 

 I will quote in full his account of the experiments that he used to 

 prove the connection between the cercaria and the adult ( Cary, 1909 : 

 612-1613). 



"On Oct. 30 a number of tadpoles of Rana catesbiana were secured 

 and several put in each jar containing infected snails. The tadpoles 

 came from a pond in the grounds of the Biological Hall of the Univer- 

 sity of Pennsylvania, where Goniobasis is not found, so it seemed improb- 

 able that they would be infected with the parasite that was found about 

 Princeton. As an added precaution all of the tissues of three of the 

 tadpoles were carefully examined without finding parasites of any kind. 

 When the tadpoles had been for a week in the jar containing the 

 encysted cereariae, a dead individual was found. This one was exam- 

 ined for the presence of parasites with the following results : Nine 

 worms, which from the condition of the sexual organs could be recog- 

 nized as young, were found in the intestine of this tadpole. The other 



