CHAP, vi ENTERIC . CANAL 335 



The digestive canal is not a simple tube of even calibre 

 throughout, but is divisible into several portions. The 

 mouth is bounded by a soft lip and leads into a small 

 buccal cavity, which communicates with a thick-walled 

 pharynx (Figs. 82 and 83, ph\ extending through about five 

 segments and connected with the body-wall by a number of 

 radially arranged muscle-fibres, the septa being absent in 

 this region. When the worm feeds, the buccal cavity is 

 everted, and the muscles serve to draw it and the pharynx 

 back again, as well as to dilate the pharynx. The latter is 

 followed by a narrow gullet or oesophagus (oes, #>), extend- 

 ing through about eight segments, and provided at about 

 the middle of its course with a pair of lateral pouches (Fig. 

 83, (z.g), with each of which, in Lumbricus, two yellowish 

 cesophageal or calciferous glands communicate posteriorly : 

 these contain a calcareous substance which may neu- 

 tralise the organic acids present in the food swallowed. 

 The pouches open into the gullet (Fig. 82, oes. gt), which 

 pass posteriorly into a dilated, thin-walled receptacle, the 

 crop (cr\ and this, again, communicates posteriorly with a 

 large gizzard (giz) with thick and muscular walls, which in 

 about the 2oth segment communicates with the intestine 

 (/*/). The intestine has a similar character throughout, and 

 extends from the gizzard to the anus : its dorsal wall is 

 folded inwards so as to produce a longitudinal ridge or 

 typhlosole (Fig. 81, typK), which serves to increase the 

 absorptive surface and in the interior of which the yellow 

 cells are very numerous. 



Certain of the cells lining the enteric canal, and especially 

 those along the typhlosole, are very granular, and like the 

 endoderm cells of the hypostome of Hydra (p. 303), are 

 to be considered as unicellular glands. They secrete a 

 digestive juice which mixing with the various substances 



