COMPLEX APPARATUS FOR NUTRITION. 97 



till they terminate in an intermediate reservoir (u), 

 which has been named the Receptacle of the Chyle. 

 From this receptacle there proceeds a tube, which, 

 from its passing through the thorax, is called the 

 Thoracic duct (t) : it ascends along the side of the 

 spine, which protects it from compression, and 

 opens, at v, into the large veins which are pouring 

 their contents into the auricle, or first cavity of the 

 heart (u) ; whence it immediately passes into the 

 ventricle, or second cavity of that organ (h). Such, 

 in the more perfect animals, is the circuitous and 

 guarded route, which every particle of nourishment 

 must take before it can be added to the general 

 mass of circulating fluid. 



By its admixture with the blood already con- 

 tained in these vessels, and its purification by the 

 action of the air in the respiratory organs (b), the 

 chyle becomes assimilated, and is distributed by 

 the heart through appropriate channels of circula- 

 tion called arteries (of which the common trunk, or 

 Aorta, is seen at a), to every part of the system ; 

 thence returning by the veins (v, v, v,) to the heart. 

 The various modes in which these functions are 

 conducted in the several tribes of animals will be 

 described hereafter. It will be sufficient for our 

 present purpose to state, by way of completing the 

 outline of this class of functions, that, like the re- 

 turning sap of plants, the blood is made to undergo 

 further modifications in the minute vessels through 

 which it circulates : new arrangements of its ele- 

 ments take place during its passage through the 

 subtle organization of the glands, which no micro- 

 scope has yet unravelled : new products are here 

 formed, and new properties acquired, adapted to 



VOL. II. H 



