20 4 



ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



where is only reached within the digestive tube of a backboned 

 animal. It may possibly be a specialized larva, like the Axolotl 

 (see vol. i, p. 249), but our knowledge is too incomplete to justify 

 such a conclusion. 



The best-known Tape-worms consist of a head, provided with 

 organs of adhesion, and passing behind into a series of flat joints 

 (proglottides), in which vast numbers of eggs are produced. The 

 complex life -history of the Common Tape- Worm 

 ( Ttznia solium) has been, briefly described else- 

 where (see vol. i, p. 441). In the adult condition 

 it lives in the intestine of man, sometimes attain- 

 ing the length of 9 feet, while in an earlier stage 

 it is found encapsuled in the muscles of the pig, 

 producing the disease known as c< measles ". 



Fig. 1152. A Simple 

 Tape -Worm (Archigetes 

 Sieboldi ), greatly en - 

 larged 



Fig. 1153. A Fish Tape-Worm (Tetrarhynchus}. A, .Adult worm, 

 enlarged, showing the four proboscides ; B, head of same still further 

 enlarged, showing double suckers, and proboscides slightly protruded; 

 c, part of a proboscis, very highly magnified, to show the hooks. 



In one small kind of Tape- Worm (Tetrarhynchus y fig. 1 153) the 

 adhesive apparatus on the head is somewhat complex, consisting 

 of two double suckers, and four tubes studded with numerous 

 hooks. When adult it lives in the intestines of fishes of the shark 

 and ray kind (Elasmobranchii). The life-history of one species 

 has been w r orked out by Herdman and Hornell, and is of particular 

 interest. In this case the host of the adult worm is a large Ray 

 (Trygon), which is common in Indian seas. The eggs pass 

 from the body of the fish, and hatch out into minute active 

 larvae, which perish unless they succeed in entering the shells of 



