26 ILLINOIS BIOLOGICAL MONOGRAPHS [472 



Therefore Cary's whole discussion in the embrological part of the paper 

 (pp. 617-647) which is based on the study of the sporocysts and the 

 cercariae developing in them cannot without further evidence be given 

 a place in the life-history of Diplodiscus temporatus. Since it proves 

 the thesis that Cary sets out to make that the embryo in the sporocysts 

 develops from parthenogentic eggs, this account is a very important 

 contribution to trematode embrology. 



Another point in Cary's paper which is very striking is the 

 great difference between the cercaria which he describes as belonging 

 to Diplodiscus temporatus and other amphistome cercariae, especially 

 that of Diplodiscus subclavatus, of which Looss has worked out the 

 life-history (Looss, 1892). A comparison of these two forms shows 

 striking differences in the shape and size of the body, in the size and 

 position of the acetabulum, in the excretory system especially that of 

 the tail, and in their activities and encystment. (Compare Cary, 1909, 

 PI. 30, Fig. 6 and Looss, 1892, PI. 20, Fig. 20). That cercariae belong- 

 ing to the same genus should be so different in structure is contrary 

 to all the accepted views of trematode development. The few observa- 

 tions found in the literature on the life-histories of closely related 

 species of trematodes show a closer structural correspondence betweeen 

 the cercariae than the adults. 



A study of Cary's material shows that he is in error in the descrip- 

 tion and drawing of the largest of the two cercariae in certain funda- 

 mental points. In his drawing (plate 30, Fig. 6) and description the 

 digestive system of the cercaria corresponds to that of the adult Diplo- 

 discus temporatus, in having pharyngeal pouches and in the muscular 

 enlargement of the esophagus at the point of division into the intestinal 

 ceca. In his material the cercaria has no pharyngeal pouches and the 

 clearly circumscribed pharynx which is followed by an enlarged portion 

 of the esophagus is entirely different from his description and drawing 

 for this form. Compare figure 27 and Plate 30, Figure 6 of Cary's 

 paper. In fact, the digestive system of his so-called cercaria of Diplo- 

 discus temporatus does not in reality correspond to that of the adult 

 as his drawing and description suggest. Cary is also in error in his 

 description of the tail of this cercaria, since the material which he 

 sent me shows that it is much longer than he figures it and has a 

 truncated end (Fig. 27). Neither does the reproductive anlage of this 

 cercaria agree with his description and drawing (p. 606, PI. 30, Fig. 6), 

 for instead of three definitely circumscribed areas two in front of the 

 acetabulum and one behind, it really consists of a small mass just in 

 front of the excretory vesicle connected with a mass in front of the 

 acetabulum by a line of nuclei. 



