242 ELEMENTARY BIOLOGY. [CHAP. 



to the hind end of the body, where it communicates with 

 the exterior by a valvular laterally compressed anus. The 

 absorptive area of the intestine is increased by the develop- 

 ment of a conspicuous intestinal-value or typhlosole which 

 lies along its whole roof, and not by a coiling of the whole 

 viscus as in the case of the Frog. 



The intestinal wall is invested in a yellowish-brown tissue 

 of so-called " chloragogen cells." This tissue (originally 

 thought to have been a kind of liver) has no sort of 

 connection with the lumen of the gut; it is intimately 

 associated with the walls of the great blood vessels, many 

 of which it completely surrounds, and there is reason for 

 regarding it as functional in the formation of an excretory 

 product which is discharged into the body-cavity, if not in 

 that of some constituent of the blood also. 



The intestinal juice of the Earthworm contains a di- 

 gestive ferment, and there open into the mouth-cavity a 

 number of small so-called "salivary" glands. Digestion 

 is nevertheless not wholly intra-intestinal, for the animal 

 when feeding vomits a digestive fluid ; this is allowed to 

 act upon the raw food material for some time, prior to its 

 ingestion. 



Digestive glands other than those just named are un- 

 known, and such diverticula of the alimentary canal as 

 remain for consideration are somewhat remarkable, and 

 little understood physiologically. There are usually three 

 pairs of oesophageal pouches, lying midway between the 

 crop and pharynx ; they are smallest in winter, and it not 

 unfrequently happens that one or more of them may be 

 absent. Occasionally, their connections with the lumen of 

 the oesophagus may become obliterated, and in rare cases 

 no trace of them is to be found. These oesophageal diver- 

 ticula are highly vascular, and contain a milk-white product 

 consisting of carbonate of lime either in a finely divided 



