28 ILLINOIS BIOLOGICAL MONOGRAPHS [474 



organs of the body were entirely free from parasites. The worms in 

 the intestine were about 2.5 mm. in length and 1 mm. in diameter at 

 the posterior end. All of them were found in the last third of the 

 intestine of the tadpole, scattered throut that part of its length. Dur- 

 ing the time that they were under examination, as was also true in 

 every other instance, the worms remained attached to the intestine of 

 the host by a large posterior sucker. The anterior part of the body 

 was in almost constant motion. 



"Others of the tadpoles used in the experiment died from time to 

 time and were examined for the presence of worms. The result of the 

 examination was identical in every case. A greater or less number of 

 worms, ranging from ten to thirty-one, was found in the posterior part 

 of the intestine. In no case were any of the worms, or any other recog- 

 nizable parasites, found in any of the other organs of the tadpoles. 



' ' The intestines of two of the tadpoles at the time of death contained 

 worms still within the cyst. Among the others, individuals of different 

 ages could be recognized so it was definitely established that the tad- 

 poles could serve as the host for the sexually mature worms. 



' ' Since it seemed probable from the number of worms found in eacli 

 of the dead tadpoles that they had in many instances been the direct 

 cause of the death of the host, some larger tadpoles were secured for 

 further experiments. These were put into jars containing encysted 

 cercariae ; but after they had remained there for a few days they were 

 transferred to a jar in which there had been no snails. A tadpole from 

 this jar was killed each week to note the development of the parasites. 

 The conditions of the environment proved unfavorable for the tadpoles 

 and the last one of them died on Jan. 19, 1909, after having been 

 infected with Diplodiscus nine weeks. The worms which were taken 

 from the intestine of this tadpole had fully developed sexual organs, 

 but, so far as could be determined from the condition of the jar, no 

 eggs had been laid, or at least no embryos had been developed." 



An analysis of these experiments shows a number of weaknesses. 

 The fact that the tadpoles came from a pond in the grounds of the 

 Biological Hall at the University of Pennsylvania offers no check on 

 the results. The location of the pond at Philadelphia and not at Prince- 

 ton and the fact that Goniobasis does not occur there, can hardly be 

 called evidence that Diplodiscus temperatus is not present in great num- 

 bers. The only check that Cary gives on his experiments is the exam- 

 ination for parasites of three tadpoles out of the whole lot. These he 

 reports free from all parasitic infection. This does not prove that the 

 others were uninfected. The three examined may have been without 

 parasites while the rest were infected, or it is even possible that the 



