533 NATURE OF REPRODUCTION. 



is formed by an involution of the walls of the second sac, presents 

 at its bottom a small globular mass, like the head of the Tsenia, 

 provided with suckers and hooks, and supported upon a short 

 slender neck. If the outer investing sac be removed, the narrow 

 canal just described may be everted by careful manipulation, and 

 the parasite will then appear as in Fig. 173, with the head and neck 

 resembling those of a Taenia, but terminating behind in a dropsical 

 sac-like swelling, instead of the chain of articulations which are 

 characteristic of the fully formed tapeworm. 



Now it has been shown, by the experiments of Kuchenmeister, 

 Siebold, and others, that the Cysticercus is only the imperfectly 

 developed embryo, or young, of the Ta3nia. When the mature 

 articulation of the tapeworm is thrown off', as already mentioned, 

 from its posterior extremity, the eggs which it incloses have already 

 passed through a certain period of development, so that each one 

 contains an imperfectly formed embryo. The articulation, contain- 

 ing the eggs and embryos, is then taken, with the food, into the 

 stomach of another animal; the substance of the articulation, to- 

 gether with the external covering of the eggs, is destroyed by di- 

 gestion, and the embryos are thus set free. They then penetrate 

 through the walls of the stomach, into the neighboring organs or 

 the areolar tissue, and becoming encysted in these situations, are 

 there developed into cysticerci, as represented in Fig. 172. After- 

 ward, the tissues in which they are contained being devoured by 

 a third animal, the cysticercus passes into the intestine, fixes itself 

 to the mucous membrane, and, by a process of budding, produces 

 the long tape-like series of articulations, by which it is finally con- 

 verted into the full-grown Tsenia. 



Prof. Siebold found the head of the Cysticercus fasciolaris, met 

 with in the liver of rats and mice, presenting so close a resem- 

 blance to the Taenia crassicollis, inhabiting the intestine of the cat, 

 that he was led to believe the two parasites to be identical. This 

 identity was, in fact, proved by the experiments of Kuchenmeister ; 

 and Siebold afterward demonstrated 1 the same relation to exist 

 between the Cysticercus pisiformis, found in the peritoneum of rab- 

 bits, and the Taenia serrata, from the intestine of the clog. This 

 experimenter succeeded in administering to dogs a quantity of the 

 cysticerci, fresh from the body of the rabbit, mixed with milk ; and 



' In Buffalo Medical Jonrml, Feb. 1853 ; also in Siebold on Tape and Cystic 

 Worms, Sydenham translation: London, 1857, p. 59. 



