

THE WORM-LIKE AXLMALS 



point of attachment to the gut, and to lengthen or shorten its body to a very con- 

 siderable extent. The chief centre of the nervous system lies in the head, and from 

 this portion, which may be called the brain, nerves pass forward to supply the 

 suckers, while a single stout cord runs backward on each side to the end of the 

 body, lying close to the edge of the segments. As already pointed out, there is no 

 trace of a mouth nor intestinal canal, although there is an excretory organ, con- 

 sisting of a ring-shaped vessel in the head, from which four tubes, corresponding in 

 position with the sucker, are prolonged backward. Two of these soon vanish, but 

 the others lying near the edges of the segments, close to the inner side of the nerve 

 cords and the longitudinal muscular band, extend to the hinder end of the body, 

 where they unite and communicate with the exterior by a common aperture. 

 At the hinder end of each of the segments these two ducts are united by a third, 

 which runs across from side to side. In addition to these structures, each 

 fully-grown segment contains a complete set of organs for the formation and 

 fertilization of eggs, of which an immense number are developed. The mature 

 segments begin at a distance of about a foot from the head, 

 and those at the hinder end of the body are the first to become 

 distended with eggs ready to hatch. The eggs, however, are 

 not laid within the human body, but the ripe segments break 

 off one by one, beginning with the last, and pass out of the 

 e intestine. The rup- 



ture is effected by 

 the contraction of 

 the muscular fi: 

 which acts upon the 

 transverse vessel of 

 the excretory system 

 of the segment in 

 front, in such a way 

 that a fresh terminal 

 pore is formed. The 

 ripe proglottis, or 

 segment ready for 

 separation, is little 

 more than a 

 that is crammed with 



minute spherical eggs, set free by the bursting of its walls. In this way the 

 eggs, which, on account of their thick protecting shell, are able to withstand the 

 most unfavorable conditions, are disseminated abroad; and. owing to their 

 numbers and minute size, some ultimately succeed in making their way in 

 connection with either food or water into the stomach of an ox. Here the egg- 

 shell is dissolved by the action of the digestive fluids, and a small embryo, the 

 prosalex, is set free. This embryo is a small round creature furnished wit- 

 books, arranged in three pairs. Upon this proscolex the gastric and intestinal 

 juices have no effect; but instead of undergoing further development in the 



HTMAX TAPEWORMS. 



(ttbuni sue) ; *, c. it. Head enlarged : e. Segments : f. Seg- 

 ment of 7~<rM safnata (eatery- 



