202 THE VITAL FUNCTIONS. 



tlie transmission of the chyle. The glands are more 

 numerous and concentrated in the Mammalia, than 

 in any other class. 



From the mesenteric glands, the chyle is con- 

 ducted, by the continuation of the lacteals, into a 

 reservoir, which is termed the receptacle of the chyle : 

 whence it ascends through the thoracic duct* which 

 passes along the side of the spine, in a situation 

 affording the best possible protection from injury 

 or compression, and opens into the great veins 

 leading directly into the heart. 



In invertebrate animals having a circulatory 

 system of vessels, the absorption of the chyle is 

 performed by veins instead of lacteal vessels. 



The sanguification of the chyle, or its conversion 

 into blood, takes place during the course of the 

 circulation, and is principally effected by the action 

 of atmospheric air in certain organs, hereafter to 

 be described, where that action, or aeration as it 

 may be termed, in common with an analogous pro- 

 cess in vegetables, takes place. In all vertebrated 

 animals the blood has a red colour, and it is also 

 red in most of the Annelida ; but in all other inver- 

 tebrate animals, it is either white or colourless-t 

 The blood derives its colour from the presence of 

 innumerable particles, corpuscles or globules, as they 

 have been called, although their usual flattened, or 

 lenticular shape better entitles them to the appel- 

 lation of blood-disks, by which they are sometimes 

 designated. These particles have long attracted 

 the attention of micrographers, as well as physiolo- 

 gists, from the difficulty that exists in determining 



* This duct is occasionally double. 



t Vauqueliii has observed that chyle has often a red tinge in 

 animals. 



