ARTICULATA. 



215 



It feeds by imbibition, (osmosis,} there being no mouth 

 or alimentary canal. The joints, or segments, are called 

 proglottides, (singular, proglottis^} and are but successive 

 growths containing ova. The life-history of these worms 

 is a curious instance of alternation of generations. The 

 fertilized ova are set free by the decomposition of the 

 joint, or proglottis. They are then swallowed by some 

 animal, and the tough capsule is dissolved, setting free 

 the embryo, which travels through the tissues of its host 

 as a little oval body, bearing weak, hook-like, or boring 

 spines. On reaching a suitable site, as the liver, it an- 

 chors, and the body dilates into a cyst, or sac full of 

 water, (Cysticercus^) Many animals, formerly known as 

 cystic worms, have been found to be but transitional 

 stages of Taeniae. In this condition the animal may 



FIG. 118. Morphology of Taeniada. a. Ovum with contained embryo, b. Cysticercus 

 longicollis. c. Head of Tsenia solium, (enlarged ;) the circlet of hooklets is at the top, 

 and below them are those of the cephalic suckers, d, A single segment or proglottis 

 magnified, i. Generating pore. 2. Water vessels. 3. Dentritic ovary, e. Portion of 

 Tape-worm, natural size, showing the alternating arrangement of the generative pores. 



remain a long while and generate new cysts by budding, 

 but when the flesh containing the " scolex," or resting- 

 larva, is eaten by some other animal, the outer wall of the 

 cyst dissolves, and becomes a true Tape-worm. The hu- 

 man Tape-worm has its cystic stage in " measly" pork, 



Of 



