56 ANIMAL FORMS 
coiled “ castings” at the entrance of the burrows. In thus 
mixing the soil and rendering it porous they are of great 
service to the agriculturist. 
Although earthworms are omnivorous they also manifest 
a preference for certain kinds of food, notably cabbage, 
celery, and meat, which leads us to think that they have a 
sense of taste. All these substances are carried within their 
retreats and devoured, or are used to block the entrance 
during the day. The food thus carried within the body is 
digested by a system (Fig. 34) composed of several portions, 
Xe. ko 0 od id 
Fig. 34.—Earthworm (Lumbricus) dissected from left side. 0, brain; ve, crop; d, 
outer opening of male reproductive system ; dv, dorsal blood-vessel ; g, gizzard ; 
h, pulsating vessels or ‘‘ hearts’; i, intestine ; X, kidney ; m, mouth; 7. c., nerve- 
cord ; oe, esophagus ; 0, ovary ; od, oviduct; ph, pharynx, 7, testes; s7., sem- 
inal receptacles ; v.v., ventral vessel. 
each of which is modified for a particular part in the pro- 
cess. The mouth (m) leads into a muscular pharynx (ph) 
whose action enables the worm to retain its hold on various 
objects until swallowed, and this in turn is continuous with 
the esophagus. From here the food is passed into the thin- 
walled crop (c),and from this storehouse is gradually borne 
into the gizzard (g), whose muscular walls reduce it to a fine 
pulp now readily acted upon by the digestive fluids. These, 
resembling in their action the pancreatic juice of higher 
animals, are poured out from the walls of the intestine into 
which the food now makes its way; and as it courses down 
this relatively simple tube the nutritive substances are ab- 
sorbed while the indigestible matters are cast away. 
5%. Circulatory system.—In all the groups of animals up 
to this point the digested food is carried over the body by 
a simple process of absorption, or in the threadworms by 
