WORMS AND CCELENTERATA 279 



platodes ("flat- worms"). We will begin with the most 

 familiar order, the tape-worms. 



There are two tape-worms especially that are parasites 

 on the human intestines, the Tcznia solium and the 

 Tcenia saginata. Both consist of a series of connected 

 segments, very narrow at the head and broadening 

 towards the end. At the end, also, the sections are 

 sexually mature, and contain a vast number of fertilised 

 eggs ; these are detached from time to time, and pass 

 out with the excrement. The sections of Tcenia solium 

 are comparatively inert after ejection, but those of 

 Teznia saginata can crawl about ; they often make their 

 own way out of the anus, and have been seen to climb 

 up the wall of a room. 



The two also differ in the armament of the head. In 

 Tesnia solium there are four suctorial disks which cling 

 to the wall of the intestine, and are assisted in this by 

 a fringe of hooks. The latter are not found in Tcenia 

 saginata, yet it is more difficult to get rid of, as its 

 suctorial disks are larger and more powerful. Often 

 a slight remedy will bring away the greater part of the 

 body, but that is no use to the patient, as the head is 

 able to form new parts. 



If the sections of Tcenia solium that contain the eggs 

 lie on the fields amongst human excrements and are 

 eaten by pigs, which do not disdain such food, the shells 

 of the eggs burst in the pig's stomach. A tiny creature 

 emerges, bores its way through the wall of the intestines, 

 and gradually reaches the muscles. Here it assumes 

 an oval shape, and forms a membrane round itself, 

 which is further strengthened by a secretion from the 



