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 into their 

 retreats and devoured, or are used to block the entrance 

 during the day. The food thus carried into the body is 

 digested by a system (Fig. 34) composed of several portions, 



FIG. 34. Earthworm (Lumbricus) dissected from left side, b, brain ; c, crop ; 

 outer opening of male reproductive system ; dv, dorsal blood-vessel ; g, gizzard ; 

 h, pulsating vessels or " hearts " ; i, intestine ; k, kidney ; m, mouth ; n. c., nerve- 

 cord ; oe, esophagus ; 0, ovary ; od, oviduct ; ph, pharynx ; r, testes ; s.r., 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 (^), 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. 



57. Circulatory system. In all the groups of animals up 

 to this point the digested food is carried through the body 

 by a simple process of absorption, or in the threadworms by 



