CESTODA. 783 



worm, still enclosed in its capsule, undergoes further important 

 changes. At one or more points in its wall a process of budding 

 takes place, each bud growing inwards in the form of a hollow 

 pocket, in the interior of which the suckers, or suckers and hooks, 

 are developed. Each bud has now the form of an invaginated 

 tape-worm head, and wlien evaginated is quite like that of the 

 adult tape-worm, differing mainly from it in being hollow. 



In other cases the cystic-worm undergoes more complex 

 changes, the buds developing not into tape-worm heads, but into 

 secondary cysts, while the buds on the secondary cysts become 

 tlie tape- worm heads, as is the case in Echinococcus cysts. 



These different kinds of cystic-worms, wliich are merely the 

 larval stages of tape -worms, have received different names. 



(1.) Cysticercus — cyst filled with serum, and provided with 



only one head. 

 (2.) Cysticcrcoid — cyst without serum, only one head. 

 (3.) Cmnurm — cyst tilled with serum, and provided with 



many heads. 

 (4.) Echinococcus, primary cyst, gives rise to secondary cysts 



filled with serum, each secondary cyst producing 



numerous heads. 

 (5.) Acephalocyst, without heads. 



Thus the tape-worm egg, when hatched, gives rise to a six- 

 hooked embryo, the six-hooked embryo changing into a cystic- 

 worm, with one or more tape-worm heads, and that is the end of 

 one part of its development. 



The cystic-worm having developed its heads, can remain for a 

 length of time without undergoing further change, cases being 

 known in which human beings have carried an Echinococcus 

 cyst for over thirty years. But if flesh, lung, liver, or brain 

 containing cystic-worms be eaten by certain animals, then a new- 

 course of development begins. The head of the young worm 

 comes out of the cyst, which is digested by the gastric juice, the 

 head being protected from the action of the juice by the carbonate 

 of lime with which it is loaded. The head is now free, attaches 

 itself to the intestinal wall, and begins rapidly to form a chain of 

 segments, which develop their sexual organs and their eggs, and 

 thus we have now the cystic- worm changed into an adult Tccnia, 



