THE WORMS 47 
tion of food, and extending deep into the tissues of the 
body, carries nutriment to otherwise isolated regions. In 
the fresh-water forms and their allies there are three main 
branches of the intestine (Fig. 28), while in many of those 
from the sea there are several, and their arrangement 
affords a basis for their general classification. 
45. Excretory system.—In the sponges and ccelenterates 
the wastes are cast out by the various cells into the gastric 
cavity or at once to the exterior with- 
out the aid of any pronounced system 
of vessels; but in the flatworms sev- 
eral of the organs are deeply buried 
within the tissues of the body and a 
drainage system becomes a necessity. 
This consists of a paired system of ves- 
seis extending the length of the ani- 
mal (Fig. 28) and provided with numer- 
ous branches, some of which open at 
various points on the surface of the 
body, while the others terminate in '-29.—Flame-cell of flat- 
x = worm (after Lane). J, 
spaces (Fig. 29, s) among the organs in flagellum ; 1, nucleus; 
what are known as flame-cells. The 8, ee soe or- 
f ‘ gaps 0. e€ body; v, 
substances which accumulate in these waste materials: 
spaces are gathered up by the flame- 
cell, poured into the space it contains, and by means of the 
vibratory motion of its flagellum (/), a movement bearing 
a fancied resemblance to the flickering of a flame in the 
wind, are borne through the tubes to the exterior. 
46. Nervous system and sense-organs.—In the sponges no 
definite nervous system is known to exist, the slight move- 
ments which the cells are able to undergo being regulated 
somewhat as they are in the Protozoa. Among the ccelen- 
terates certain of the cells scattered over the surface of the 
body are set aside as nerve-cells, and, more or less united by 
means of fibers extending from them, convey impulses over 
the body. In the flatworms the larger number of nerve-cells 
