328 THE EARTHWORM chap, 



neutralised by the calcareous secretion of the oesophageal 

 glands — dissolves the proteids and other digestible parts so 

 as to allow of their absorption. It is very probable that 

 the process is purely extra-cellular or enteric, the food being 

 dissolved and rendered diffusible entirely in the cavity of the 

 canal (p. 300). By the movements of the canal — caused 

 partly by the general movements of the body and partly 

 by the contraction of the muscles of the canal and septa, 

 aided by the action of the cilia, the contents are gradually 

 forced backwards and the earth and other indigestible 

 matters are expelled at the anus. 



The coelome is filled with a colourless transparent cxlomic 

 fluid in which are suspended amoeboid corpuscles or leuco- 

 cytes Uke those of the frog's blood and lymph (p. 105). The 

 function of this ccelomic fluid is probably to distribute the 

 digested food in the enteric canal to all parts of the 

 body. In Hydra, where the lining wall of the digestive 

 cavity is in direct contact with the simple wall of the 

 body, the products of digestion can pass at once by 

 diffusion from endoderm to ectoderm ; but in the present 

 case a means of communication is wanted between the 

 enteric epithelium and the comparatively complex and 

 distant body-wall. The peptones and other products of 

 digestion diffuse through the enteric epithelium into the 

 ccelomic fluid, and by the continual movement of the 

 latter — due to the contractions of the body-wall — are 

 distributed to all parts. Thus the external epithelium 

 and the muscles, as well as the nervous system and re- 

 productive organs not yet described, are wholly de- 

 pendent upon the enteric epithelium for their supply of 

 nutriment. 



The earthworm, like the frog, possesses a series of blood- 



