475] LARVAL TREMATODES—CORT 29 



parasites may have been overlooked. Any man even if somewhat accus- 

 tomed to examinations for parasites is likely to overlook them, especially 

 if they are small and the infection light, until a chance finding' directs 

 his attention to a particular organ. Therefore it would seem that the 

 above experiments were not sufficiently controlled to prove that no infec- 

 tion of Diplodiscus temporatus was present in the tadpoles previous to 

 the experimental feeding. 



For infection he puts the tadpoles in the jars with infected snails 

 and when a week later one of the tadpoles proved to be infected with 

 nine immature specimens of Diplodiscus temporatus he concluded that 

 they had developed from the larvae in the snails. A comparison of 

 the structure of the two forms shows how improbable this is. The 

 largest cercaria of this type in the alcholic material, which Cary sent 

 me, had a body, 0.40 mm. in length and 0.20 mm. in width and an 

 acetabulum 0.065 mm. in diameter. The only measurements that Cary 

 gives in his description, which were evidently taken from a living speci- 

 men, are 2 mm. in length for both body and tail and 0.15 mm. in width. 

 The tail is usually at least as long as the body, so that would make 

 the body of the cercaria not over 0.1 mm. in length. Cary gives no 

 measurements for the acetabulum but his drawing (PI. 30, Fig. 6) shows 

 it less than half the width of the body. 



Since the cercariae must have had about the size, shape, and propor- 

 tions given above at the time this tadpole was supposed to have eaten 

 the cysts, their metamorphosis surely must have been extraordinary to 

 have developed in a week into the immature specimens of Diplodiscus 

 temper -at us, which Cary found in the tadpoles. He describes these forms 

 as 2.5 mm. in length, 1 mm. in diameter at the posterior end, and as 

 being attached by the typical large posterior sucker. The posteror 

 sucker of the young Diplodiscus temporatus (Fig. 28) has practically 

 the width of the posterior end, which in this case would be almost 1 mm. 

 Therefore if Cary's contention be correct his cercariae in one week 

 almost tripled their length, changed the whole shape of the body, and 

 increased their width five times. The acetabulum must in some way 

 have jumped from the center of the body to the posterior extremity 

 and increased its diameter ten times. Since such a transformation is 

 impossible one is forced to conclude that the tadpoles used in the experi- 

 ments were already infected with Diplodiscus temporatus, and that 

 there is no connection between this species and the cercariae used in the 

 experiment. The fact that according to Cary every tadpole examined 

 was infected with Diplodiscus temporatus cannot be taken as attesting 

 the success of the experiments but merely the general uniformity of 

 the original infection. A detailed comparison of figures 27 and 28 



