ORGANS OF ALIMENTATION. 51 



In tliis way the animal lays hold of the various ol)jects, nutri- 

 tious and otherwise, which it devours or draws into its buri-ow. 



Embedded in the muscular walls of the pharynx are a 

 number of small " salivary " glands of wliose function notliing 

 is definitely known, thougli they doubtless 2)our a digestive fluid 

 into the pharyngeal cavity. 



2. The oesophagus (ce), a slender, thin- walled tube extendino" 

 from the 6tli to the loth somite. Through this the food is 

 sw^allowed, being driven slowly along by wavelike (jjeristaltic) 

 contractions (p. 55). In the region of the lltli and 12t}i 

 somites are three pairs of small pouches opening at the sides of 

 the oesophagus. These are the calciferous glands {c.gL). They 

 contain solid masses of calcium carbonate, and Darwin conjec- 

 tures that their use is partly to aid digestion by neutralizing tlie 

 acids generated during the digestion of leaves, and i)erhaps 

 partly to serve as an outlet for the excess of lime in the body, 

 especially when worms live in calcareous soil. 



3. The crop (<?), about the 16th somite; a thin-walled, sac- 

 like dilatation of the alimentary canal, which serves as a reser- 

 voir to receive the swallowed food. 



4. The gizzard (g), about the iTth somite; a cylindrical, 

 firm and muscular portion, lined by a horny membrane. In this 

 the food is rolled about, squeezed and ground to prepare it for 

 digestion in the following portion, viz. : 



5. The stomach-intestine (s.i.), which corresponds physio- 

 logically to both the stomach and intestine of higher animals. 

 This is a straight thin- walled tube, extending from the gizzard 

 to the anus, without convolutions, not difi'erentiated into stomach 

 and intestine, and devoid of distinct glandular appendages sui-h 

 as the liver or pancreas existing in the higher animals. The 

 digestive fluid is secreted by the w^alls of the alimentary canal 

 itself, the surface of which is much increased l)y the presence of 

 lateral pouches or diverticula, one on either side in eacli somite. 

 In front these are large and conspicuous, l)ut behind they gradu- 

 ally diminish in size until scarcely percei)tible. 



The inner surface of the stomach-intestine is further increased by a 

 deep inward fold, called the typJiJosole, running longitudinally along the 

 dorsal median line. The typhlosole is not visible on the exterior, but is 

 seen by opening the stomach-intestine from the side or below, or upon 



