6 Earle C. Stevenson 



the cavity of the hook. From these observations, he concluded 

 that the hooks might function as suctorial organs. After exam- 

 ination of a large number of hooks, both of Cystic ercus pisifor- 

 mis, and of the adult Taenia serrata, however, I have found no 

 such openings in them. 



The position of the hooks on the head and the manner in which 

 they are found imbedded in the tissue of the intestine demonstrate 

 that they are essentially organs of attachment. 



life history of T. serrata and T. serialis 



The gravid segments, escaping with the feces, carry the eggs 

 which constitute the source of new infections. The eggs are con- 

 veyed in food or water into the stomach of the hare, where the 

 action of the fluids of the stomach destroys the shell, thus releas- 

 ing the embryo, which bores through the intestinal wall. The 

 onchosphere, according to Kuchenmeister (1857), may be either 

 passive or active in its migrations to parts of the body, after 

 penetrating the wall of the alimentary canal. Embryos have been 

 found in the blood by Leuckart, and in such cases would be as- 

 sisted in movements by the blood current. 



The onchosphere at the time of its migration possesses six 

 minute hooks (5 to 7 f* in length) which are used in burrowing 

 through the tissues. These hooks, according to Leuckart, are 

 either lost when the embryo is in the blood or are soon cast off 

 after encystment. The following account of the development of 

 the permanent crown of hooks is taken from Leuckart, Kuchen- 

 meister, and Wagener. 



The encysted stage in the life history of T. serrata is known as 

 Cysticcrcus pisiformis, and of- T. serialis as Coenurus serialis. 

 During the formation of this stage, the adult crown of hooks is 

 developed. Papillae appear on the epithelial coat at the bottom 

 of the flask-shaped cavity which represents the beginning in the 

 embryo of the head of the adult parasite. These papillae become 

 elongated into hollow cones, the walls of which are membranous. 

 These membranous cones, though at first very delicate and fragile, 

 become hard and resistant by the deposit of chitin in successive 



196 



