140 HELMINTHOZOA. 



mentary canals of new fishes ; and it is only under such circumstances 

 that they seem to attain their full development. 



(367.) CYSTOIDEA. Transformation of Cystiform Entozoa into Taenia?. 

 The gradual transformation of Cysticercus pisiformis into the Tcania 

 serrata has been established by feeding young dogs with the cystic 

 parasites still enclosed in the cysts in which they are found in the 

 omentum of rabbits*. The first effect produced upon the Entozoa 

 thus enclosed in their cysts, after they have been swallowed, is the solu- 

 tion of the cysts by the gastric juice in the dog's stomach, after which 

 the caudal vesicle of the Cysticercus pisiformis is attacked and de- 

 stroyed by the same digestive agent, leaving nothing of it remaining 

 but the whitish and rounded Scolex, which, passing through the py- 

 lorus, becomes attached to the walls of the duodenum, in which situation 

 it has to await its subsequent growth. At the posterior end of the now 

 tailless cyst-worm, the point at which the caudal vesicle was previously 

 attached is distinctly indicated by a sort of cicatrix. Subsequently the 

 growth of the Entozoon commences, its transverse wrinkles are mul- 

 tiplied, and in the course of a few days the body becomes divided into 

 segments, which, at first very short, elongate and soon present the 

 marginal generative pores. After a residence of twenty-five days in 

 the intestines of the dog, the Taenia has attained the length of from 10 

 to 12 inches, and in three months 20 or 30 inches or more, at which 

 time the posterior joints appear to be sexually matured, and the last 

 segments (Proglottides) become detached. The ova enclosed in the 

 ripe joints are seen to be completely developed, and contain in their in- 

 terior the mobile embryo armed with its six booklets. 



It must now be an important task for helminthologists to trace the 

 further development of the embryos produced from these eggs, in order 

 to determine the mode of origin of the Cysticercus pisiformis. 



(368.) The Echinococcus veterinorum, long considered as a distinct 

 Entozoon,is in reality merely a hydatid cyst filled with the larvas (Scoleces) 

 of Taenioid worms ; it occurs in the liver, the cavity of the abdomen, the 

 heart, the voluntary muscles, and the ventricles of the brain of man, 

 in the liver, lungs, &c. of the ox, sheep, goat, ape, pig, &c. The walls 

 of the true cysts consist of numerous concentric layers or plates, re- 

 sembling those of colloid cells. The liquid existing within them is 

 yellowish or reddish, and albuminous. The larvaB appear to the naked 

 eye as minute white opake specks, varying in size from about -^^" to 

 -j-J-y " in length ; they also vary greatly in form : when the head is 

 retracted, they appear more rounded than when it is protruded. The 

 hooks surrounding the anterior end of the body consist of a basal por- 

 tion, an internal transverse blunt tooth, and a curved terminal portion 

 or claw ; they are about y-^Vo" to Win/' ^ n l en g tn - I* 1 some of the 



* Vide De Cysticercorum in Tsenias Metamorphosi pascendo, experimenta in In- 

 stitute Physiologico Vratislaviensi administrata, Auctor G. Lowald : Berolini, 1852. 



