THE WORMS 



53 



or crawling. They also give support to a brain, which is in 

 the form of a collar encircling the pharynx near the head, 

 and to the great nerves which extend from it. Still fur- 

 ther within the transparent body the alimentary canal may 

 be distinguished as a straight tube 

 passing directly through the ani- 

 mal. The alimentary canal lies 

 freely in a great space, the body 

 cavity, traces of which may exist 

 in the flatworms in the form of 

 hollow spaces into which the 

 kidneys open. It is possible that 

 in this form also the kidneys open 

 into this space, and it is roomy 

 enough besides to afford lodg- 

 ment for the reproductive organs 

 in addition to a large amount of 

 fluid which is probably somewhat 

 of the nature of blood. A space in 

 some respects similar to this occurs 

 in all the animals above this group, 

 and as we shall see, it is often cu- 

 riously modified and serves for a 

 number of different and highly im- 

 portant purposes. In the round- 

 worms the fluid it contains proba- 

 bly acts in the nature of a blood 

 system, distributing the food and 

 oxygen to various parts of the body and carrying the wastes 

 to the kidneys for removal. 



53. Multiplication. In the matter of the production of 

 new individuals the greatest differences exist. In some 

 threadworms, for example the " vinegar eel," eggs develop 

 within the body and the young are born with the form of the 

 parent. In other cases the eggs are laid in the water, where 

 they, too, may directly grow to the adult condition ; but in 



FIG. 32. Thread- or round- 

 worms. A, vinegar eel ( An- 

 guittuld) ; m, month ; ph., 

 pharynx ; i, intestine ; ov.. 

 developing young. B, Tri- 

 china. From Nature, greatly 

 enlarged. 



