ANNULOIDA SCOLECIDA. 83 



The whole system communicates with the exterior by an 

 aperture placed at the extremity of the last joint. 



The head, by a species of budding, develops a series of 

 flattened joints, each of which contains male and female 

 organs. The joints nearest the head are always the 

 newest, the mature joints being situated at the other 

 extremity. The compound animal thus formed is often 

 several yards long. 



Each segment contains a large number of ova; but 

 these are never hatched within the animal inhabited by 

 the tape-worm. The mature joints gradually break off, 

 and pass from the intestine; and the minute ova con- 

 tained therein are swallowed by some warm blooded 

 animal. In the case of the human tape-worm, the ova 

 find their way into the stomach of the pig, where they 

 are hatched. The embryo, by means of the flinty hooks 

 with which its head is furnished, makes its way through 

 the walls of the stomach, into the muscles. In this situa- 

 tion it develops at its lower extremity a bladder-like sac, 

 filled with fluid. When it abounds in the flesh of the 

 pig, the pork is said to be measled. These " measles " 

 were formerly called cystic (Gr. kustis, a bladder) worms, 

 and were bqlieved to be different animals. These cystic- 

 worms, so long as they remain in the tissues of the pig, 

 never breed tape-worms, nor develop ova, but they are 

 said to be able to multiply their own kind by budding. 

 When a quantity of measly pork is eaten, a cystic-worm 

 is sometimes transferred to the human stomach. It 

 fastens itself by its hooks and suckers to the intestine, 

 loses its bladder, and commences to develop 'joints by 

 budding, and finally produces a tape-worm. 



Another species of human tape-worm is derived from 

 " measles " found in the muscles of the cow. The cystic- 

 worms found in the tissues of the mouse and rat produce 

 tape- worms in the intestines of the cat ; and the cystic- 

 worm which causes the disease called staggers in sheep, 

 when transferred to the stomach of the dog, is developed 

 into a tape-worm. 



