ANNELIDA : THE EARTHWORM, NEREIS 221 



and sixth segments, but pushes the latter backwards as far 

 as the seventh. Numerous strands of muscle run from it to 

 the body-wall. Behind it lies the oesophagus, a straight, 

 narrow, thin-walled tube, which extends to the fourteenth 

 segment. In the eleventh segment it bears at the sides 

 a pair of (esophageal pouches, and in the twelfth two pairs 

 of oesophageal glands. These contain large cells which 

 secrete calcium carbonate and pass it through the pouches 

 into the oesophagus. In the fifteenth and sixteenth 

 segments the oesophagus expands into a large, thin- walled 

 crop, which in turn communicates behind with the gizzard, 

 another swelling, with thick muscular walls and a horny 

 lining, in segments 17 and 18. From the gizzard to the 

 anus runs a wide, thin-walled tube known as the intestine. 

 The intestine is narrowed where it passes through the septa, 

 and its dorsal wall is infolded to form a longitudinal ridge 

 known as the typhlosole. The gut is lined with a layer of 

 columnar epithelium, outside which are thin longitudinal 

 and circular muscular layers, covered by the ccelomic epi- 

 thelium, which here consists of the yellow cells. These 

 are large and contain yellow granules of an excretory 

 product. They fall off into the ccelomic fluid, and there 

 break up and set free their granules. The typhlosole is 

 filled with yellow cells. 



Food is drawn into the mouth by a sucking action of the 

 muscular pharynx, passed along the oesophagus, stored in 

 the crop, ground up in the gizzard with the aid of small 

 stones which have been swallowed, and in the intestine first 

 digested by juices secreted from the epithelium, and then 

 absorbed. The surface for these purposes is increased by 

 the presence of the typhlosole. The function of the secretion 

 of the oesophageal glands is uncertain. It has been supposed 

 to be an excretion of the calcareous matter, which is very 

 plentiful in the dead leaves, of which the food is largely 

 composed. Probably it has some further function, whether 

 this be the neutralisation of the acids of the food, or, as 

 seems to be the case, the removal of carbon dioxide in the 

 form of calcium carbonate. 



The earthworm has a well-developed central nervous 

 system which consists of (1) a pair of suprapharyngeal 

 ganglia, rounded bodies lying above the mouth, and 



