THE WORMS 



rr^HE worms include a large number of creatures which differ 



greatly one from another, both in form and in habits of life. 

 They are found in almost every imaginable situation, although 

 generally dependent upon moisture for their development. Many 

 sorts of worms are parasites, and no animal is wholly free from 

 their attacks. 



Although repulsive at first sight, worms are really among the 

 most interesting of all animals, for a careful study of their develop- 

 ment and structure shows that crustaceans, insects and mollusks are 

 probably descended from worm-like ancestors. 



The flatworms or Platodes are among the simplest of all worms. 

 The free-swimming flatworms are common upon seaweed-covered 

 rocks, or upon dead shells. They are generally small creatures 

 more or less leaf-shaped with the front end of the body bluntly 

 rounded. They crawl or swim with a wave-like motion. The sucker- 

 like mouth is upon the lower surface, never at the extreme front of 

 the creature; and the intestine ends blindly, so that undigested 

 particles of food are cast out through the mouth. Numerous little 

 eye-spots and sensory hairs are often seen on the upper surface of 

 the worm, and the nervous system is well develojDed. The brain is 

 near the front end, and gives rise to two main nerve branches which 

 extend down the body near the lower surface and are joined at regu- 

 lar intei'vals by cross fibres, making a ladder-like arrangement. 

 The flatworms often lay their eggs in cocoons or capsules, each cap- 

 sule containing a considerable number of eggs, only a few of which 

 develop ; the remainder being devoured by the successful larvae. 



The tapeworms and flukes are related to the flatworms, and are 

 parasitic within many animals. The development of these para- 

 sites is interesting, for example the tapeworm produces eggs which 

 develop into little embryos, each with four or six hooks and suckers, 

 and which are then cast out and die, unless accidentally swallowed 

 by some other animal. In this event, however, the little tapeworm 

 gets rid of its egg-shell, and bores its way through the wall 



