CHAP, vi ENTERIC CAXAL 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 (esophagus (as, ce), extending through 

 about eight segments, and provided at about the middle 

 of its course with a pair of lateral pouches (Fig. 83, ce. 

 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. gl), 

 which pass posteriorly into a dilated, thin-walled recep- 

 tacle, the crop (cr), and this, again, communicates 

 posteriorly with a large gizzard (giz) with thick and 

 muscular walls, which in about the 2Oth segment com- 

 municates with the intestine (int). The intestine has a 

 similar character throughout, and extends from the 

 gizzard to the anus ; it is ciliated and its dorsal wall is 

 folded inwards so as to produce a longitudinal ridge or 

 typhlosole (Fig. 81, typh), 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- 33). a*" 6 to be considered as unicellular glands. 

 They secrete a digestive juice which mixing with the 



