24 



GUIDE TO THE STUDY 



the intermediate host is the rabbit, and it should be understood 

 that while the general features of the life cycle are typical for 

 the group, the details apply to this species only. 



Development within the Liver. — The liberated embryos, by 

 means of their armature of hooks, penetrate the walls of the intes- 

 tine and are carried by the blood current to the liver. There they 

 lose their hooks and by the sixth day they have enlarged suffi- 

 ciently to appear as little transparent vesicles (Fig. 7). By the 

 twelfth day, having attained a size of 3 mm., they present the 

 appearance shown in the slides provided, that of little whitish 



Fig. 8. — Migratory larvae of Tcenia pisiformis as they may be found free in the 

 body cavity of the rabbit 5 weeks after infection. (Orig.) 



bodies made up of a very loose parenchyma tissue, limited by a 

 delicate cuticle. The head of the future tapeworm begins to 

 form at this stage. 



Development in the Mesenteries. — About a month after infesta- 

 tion the very active larva squirms out from the liver and lives 

 free in the body cavity of the rabbit for several days (Fig. 8). 

 The central part of the larva degenerates and becomes filled with 

 a fluid, and the rounded mass attaches to the peritoneum or 

 mesenteries of its host as a cysticercus. This cysticercus, 

 with its invaginated head of the future tapeworm, at the end of 

 a few weeks is about the size of a pea, and is ready to transfer 

 to the definitive host and there develop into the mature tapeworm. 

 This process requires about two months before ripe segments 

 are ready to be discharged. 



