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. This latter system lies freely 
in a great space, the body cavity, 
traces of which may exist in the 
flatworms in the form of small hol- 
lows among the organs 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 
lodgment for the reproductive or- 
gans 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 
Fie. 32, — Thread- or round- 
number of different and highly im- worms. A, vinegar eel (An- 
portant purposes. In the round- — ¥dula); m, month; ph, 
A é ae pharynx ; i, intestine ; ov., 
worms the fluid it contains proba- developing young. B, Tri- 
bly acts in the nature of a blood —“#a. From Nature, greatly 
enlarged. 
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 
