Chap, xii.] OF DIGESTION. 181 



colour in the stomacli and changing into a greyish homogeneous 

 matter.! While worms swallowed by the hydras underwent a 

 similar transfigurement. 



Moreover, Schweiger found in the digestive cavity of polypi, 

 and in thQ canals connecting the individuals aggregated as a 

 colony, a lactescent liquid, probably a nourishing liquid. It is 

 this liquid which is absorbed by the animal, and which circulates 

 through its organism, there where the stomach emits canalicules 

 with csecums, or even a sort of complete system of canals, as in 

 the medusa.^ 



The isomeric metamorphosis of the albuminoids is therefore 

 accomplished even in the rudimentary beings, but it demands 

 for that purpose a time so much the longer as the living labora- 

 tory is the more imperfect. Thus after seveu or eight days of 

 abstinence food is still found in the digestive tube of caterpillars. 

 Schweiger says that he found in the intestine of leeches blood 

 sucked two-and-a-half years before. This extreme slowness of 

 the digestive labour in the inferior animals helps us to under- 

 stand how they are able to resist abstinence so long. 



Absorption is slow in the digestive cavity of the inferior in- 

 vertebrates, and, naturally, the movement of the alimentary 

 mass is also very slow there. The contractility of the walls • is 

 aided in many of these animals by vibratile cilia, that is to say, 

 epithelial cells, furnished with long mobile ciliary prolongations. 

 These filifprm appendices form on the stomachal and intestinal 

 surface of numerous invertebrates a sort of living meadow where 

 each blade is animated by a regular oscillatory movement, 

 eflfected always in the same direction, and powerfully aiding the 

 conveyance of the aHmentary substances. This arrangement of 

 the intestinal epithelium, frequent among the invertebrates, is 

 also observed in the foetal state among the selacians, the batra- 

 chians, and so on; but it is regularly lacking in birds and 

 mammifers even at the embryonary period.' 



1 Dugfes, loo. cit., p. 331. ^ HaMdbueh der Natv/rgeachichte. 



s Leydig, loc. cit., pp. 348, 375. 



