336 THE EARTHWORM CHAP. 



various substances containing organic acids taken in by 

 the mouth and said to be neutralised by the calcareous 

 , secretion of the cesophageal glands dissolves the proteids 

 and other digestible parts so as to allow of their absorp- 

 tion. 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. 305). 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 gradu- 

 ally forced backwards, and the earth and other 

 indigestible matters expelled at the anus. 



The ccelome is filled with a colourless transparent 

 ccelomic fluid in which are suspended amoeboid corpuscles 

 or leucocytes like 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 ex- i 

 ternal epithelium and the muscles, as well as the nervous 

 system, reproductive and other organs not yet described, 

 are wholly dependent upon the enteric epithelium for 

 their supply of nutriment. 



The earthworm, like the frog, possesses a series of 



