ORGANS OF ALIMENTATION. 51 



In tliis way the animal lavs hold of the various objects, nutri- 

 tious and otherwise, which it devours or draws into its burrow. 



Embedded in the muscular walls of the pharynx are a 

 number of small 4 ' salivary ' ' glands of whose function nothing 

 is definitely known, though they doubtless pour a digestive fluid 

 into the pharyngeal cavity. 



2. The oesophagus (#?), a slender, thin-walled tube extending 

 from the 6th to the 15th somite. Through this the food is 

 swallowed, being driven slowly along by wavelike (peristaltic) 

 contractions (p. 55). In. the region of the llth and 12th 

 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 bv neutralizing the 



i/ O i/ O 



acids generated during the digestion of leaves, and perhaps 

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

 especially when worms live in calcareous soil. 



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

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



v 



yoir to receive the swallowed food, 



4. The gizzard (</), about the 17th 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 differentiated into stomach 

 and intestine, and devoid of distinct glandular appendages such 

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

 digestive fluid is secreted by the walls of the alimentary canal 

 itself, the surface of which is much increased by the presence of 

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

 In front these are large and conspicuous, but behind they gradu- 

 ally diminish in size until scarcely perceptible. 



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

 deep inward fold, called the typhlosole, 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 



