TYPES OF TAPEWORM LARVM 235 



Having reached the organ or tissue in which it is destined to 

 develop, the embryo loses its hooks and grows into some form of 

 bladderworm, that is, the body undergoes a series of transfor- 

 mations which usually result in the formation of a bladder-like 

 body filled with a watery fluid. Into the bladder there grows 

 an invagination and at the bottom of this, pushed inside out into 

 it, there develops a head or scolex. There are different types 

 of bladderworms which go under different names, as follows: 



(1) the cysticercus (Fig. 86A), the simple type described above; 



(2) the cysticercoid (Fig. 86B), in which the bladder part of the 



FIG. 86. Types of tapeworm larvae: A, cysticercus of Tcenia solium with head 

 and neck evaginated, X 3; B, cysticercoid of Hymenolepis nana, X 12; C, plerocer- 

 coid of Dibothriocephalus latus, with head invaginated. (A, partly after Stiles, B, 

 from several figs, by Grassi and Rovelli; C, partly after Braun.) 



worm is poorly developed; (3) the ccenurus, in which multiple 

 heads form in the single bladder; and (4) the hydatid, in which 

 the bladder buds into multiple daughter cysts, each with multiple 

 heads (Fig. 95). The larvae of the tapeworms of the family 

 Dibothriocephalidce are quite unlike the bladderworms of other 

 tapeworms. They grow as long wrinkled wormlike bodies with 

 the head invaginated in a little projection at the anterior end. 

 Such a larva is called a plerocercoid (Fig. 86C). 



When the organs or tissues in which the larval stages are 

 developed are eaten by an animal of the kind from which the eggs 

 originally came, all but the scolex of the bladderworm is digested 

 off, the latter turns right side out, attaches itself to the wall of 

 the small intestine with the aid of its suckers and hooks, and be- 

 gins to bud off proglottids of another generation. Tapeworms 

 are usually looked upon as inert animals, but in reality they are 

 quite active, and their movements can often be felt. 



