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 bnccal 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 i 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 (ces, 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 cdlciferous 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 

 passes 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 (int). The intestine has a similar char- 

 acter 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 : it is wanting in the last segment. 



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)> are to be considered as unicellular glands. 

 They secrete a digestive juice which mixing with the 



