306 



ILLINOIS BIOLOGICAL MONOGRAPHS 



[306 



Frequency of occurrence in the above table has been determined by taking 

 the sum of the number of localities from which the species has been reported 

 (including times from same locality) or in case it occurs in more than one host 

 in one locality the number of host species is added. Numbers are approximate. 



LIFE HISTORY OF THE PROTEOCEPHALIDAE 



Since the appearance of a previous paper by the writer (La Rue 

 1909) in which he reviewed the literature on thus subject and in which 

 he outlined certain feeding experiments which had for their object the 

 solution of the problem of the life history of the cestode infesting 

 Amblystoma tigrinum but little additional data have appeared on the 

 life history of Proteocephalids. Barbieri (1909) found that Bythro- 

 trephes and Leptodora act as intermediate hosts for Proteocephalus 

 agonis. So far as can be ascertained there are no other data in the 

 recent literature of this subject. Fuhrmann (1903) outlined the life 

 history of Proteocephalids. Several of the older investigators have 

 mentioned the finding of plerocercoids in the livers of fish which har- 

 bored species of Proteocephalus in the intestine. The writer (La Rue 

 1909) recorded the finding of many plerocercoids in the tissues of the 

 salamander, Amblystoma tigrinum, and the positive results obtained 

 from feeding these plerocercoids to uninfected hosts. The probability 

 was there suggested that salamanders might become infected through 

 the eating of infected salamanders. There is at present no reason for 

 changing this view. While making an examination of a specimen of 

 Natrix rhombifcr the writer found numerous encysted plerocercoids in 

 the tissues of the alimentary tract and of the liver. Since many snakes 



