307] PROTEOCEPHALIDAE—LA RUE 307 



are accidental or intentional cannibals it is possible that the eating of 

 one snake by another may be one method of infection. Since also this 

 species of snake lives largely upon fish and frogs one should look to 

 these food animals for the intermediate host of its cestodes. No avail- 

 able records deal with this method of infection. 



From the data presented by various workers it seems probable that 

 the life history of the Proteocephalids is essentially as follows : The 

 eggs and some of the ripe proglottids bearing eggs are voided by the 

 host into the water where they are eaten by an invertebrate, perhaps a 

 worm, an insect larva, or a crustacean, or possibly the eater is a verte- 

 brate, fish, snake or an amphibian of the same species as the host or 

 different. If the invertebrate or vertebrate furnishes a suitable habitat 

 for the development of the parasite the six-hooked embryo establishes 

 itself and from it develops a plerocercoid about which the host produces 

 a cyst. If the intermediate host be eaten by a vertebrate which furnishes 

 a proper habitat for the adult parasite the plerocercoid when it is 

 released by the action of the digestive juices from its intermediate host 

 and from its cyst passes to the intestine and develops into the adult 

 tapeworm. If the final host engulfs material containing eggs of the 

 cestode harbored by itself or its congeners or perhaps by members of 

 other species the host becomes infected with the plerocercoids and so it 

 may function as a secondary as well as a primary host for its parasitic 

 species. Cannibalism may be a means in the spread of the parasites 

 harbored. The problems connected with the life-history of these para- 

 sites must ultimately be settled by experimental methods. 



ORIGIN OF THE PROTEOCEPHALIDAE 



This work has thrown some light on the relations of the genera and 

 species of Proteocephalidae to one another. It is of interest to attempt 

 to point out the probable relations of the family to other cestodes. Like 

 many other cestodes the members of this family were once included 

 in the great genus Taenia. That, however, was before the internal 

 structures of these cestodes were well known and it seems that the basis 

 for this classification was the apparent similarity of the suckers. It is 

 now evident that the Proteocephalids are most closely related struc- 

 turally to the cestodes of the order Tetraphyllidea. A marked agree- 

 ment in the general arrangement of all the internal organs of Tetraphyl- 

 lidean cestodes is to be noted. In these respects the Proteocephalids 

 do not agree with the Cyclophyllidea. In external features alone the 

 Proteocephalids resemble the Cyclophyllidea more than the Tetraphyl- 

 lidea. This is due to the marked simplicity of the heads and suckers of 

 the Proteocephalids and the usual hemispherical form of the suckers. 



