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PL A THELMINTHES. 



the stomach the larvae with their six hooks bore through the intes- 

 tinal wall and migrate, using the blood-vessels in their course, into 

 the muscles, or more rarely other organs. Here they develop 

 into bladder worms (cysticerci). In this they become oval and 

 secrete a cyst to which, as a foreign body, the pig adds an envelope 

 of connective tissue. The cysticercus blastema grows through 



Fio. 247. Structure and development of the cysticercus (C. cellulosae of Tcenia 

 solium). a, measly meat, natural size; below an escaped cysticercus; 6, cysticer- 

 cus, with exserted scolex, enlarged; c-e, development of the scolex, more en- 

 larged; c, young cysticercus with blastema of scolex (above) and water- vascular 

 net ; d, e, different stages of scolex in receptaculum, the cysticercal wall mostly 

 removed. 



increase of cells, but more by the infiltration of serous fluid, so 

 that it becomes distended into a delicate translucent vesicle. So 

 abundant can this be that in T. solium the microscopically small 

 embryo can grow in three or four months to the size of a bean or 

 pea; in other species as large as a hen's egg. By invagination the 

 wall of the bladder produces the blastema of the scolex (fig. 247, c). 

 This has at first a sac-like shape, but soon increases in length, its 

 growth being confined by an envelope, the receptaculum (d), so 

 that it is bent. 



At the apex of this blind sac arises the characteristic armature 

 of the scolex which makes it possible to say what tapeworm will 

 come from the cysticercus. Thus in T. solium there are four 

 suckers and a crown of hooks. These parts are at first inverted 



