BRANCH YERMES: THE WORMS 139 



The common tapeworm of man, Tcenia solinm (there 

 are several other species of Tcenia which infest 

 man, but solium is the common one), may serve as an 

 example of the group. In the adult condition its body, 

 which is found attached to the inner wall of the intestine, 

 is like a long narrqw ribbon : it may be two or three 

 metres long. It is attached by one end, the head, which 

 is very small and provided with a score of fine hooks. 

 Behind the head the thin ribbon-like body grows wider. 

 The body is composed of many (about 850) joints called 

 proglottids. There is no mouth or alimentary canal, the 

 liquid food being simply taken in through the skin. Each 

 proglottid produces both sperm-cells and egg-cells ; one 

 by one these proglottids or joints with their supply of 

 fertilized eggs break off and pass from the alimentary 

 canal with the excreta. If now one of these escaped 

 proglottids or the eggs from it are eaten by a pig, the 

 embryos issue from the eggs in the alimentary canal of 

 the pig, bore through the walls of the canal and lodge in 

 the muscles. Here they increase greatly in size and 

 develop into a sort of rounded sac filled with liquid. If 

 the flesh of the pig be eaten by a man, without its being 

 first cooked sufficiently to kill the larval sac-like tape- 

 worms, these young tapeworms lodge in the alimentary 

 canal of the man and develop and grow into the long 

 ribbon-like many-jointed adult stage. 



The life-history of the other tapeworms which infest 

 the various vertebrate animals is of this general type. 

 There is almost always an alternation of hosts, the larval 

 tapeworm living in a so-called intermediate host, and the 

 adult in a final host. Of the domestic animals the dog 

 is the most frequently attacked. At least ten different 

 species of tapeworms have been found in the dog. The 

 intermediate hosts of these dog tapeworms include 

 rabbits, sheep, mice, etc. Some of the domestic fowl, 



