CHAPTER THIRD. 



SANGUIFEROUS SYSTEM. 

 FIRST SECTION. 



General observations on the sanguiferous system. 



THE materials elaborated by the digestive organs and 

 conveyed by the lacteals to the blood, are sent for the nu- 

 triment of each point of the body, by a vascular apparatus 

 almost as universal in the animal kingdom as that of diges- 

 tion itself, and presenting phases of development, in its 

 essential parts, as regular and progressive, as its general 

 form is varied and diversified in the different tribes. As 

 the fountain of all nourishment and of all development is 

 the blood, the peculiarities of this hydraulic apparatus in 

 the different classes, and the laws which regulate its distri- 

 bution in different animals, and in different parts of the 

 body, involve the chief mystery of their development and 

 form. Half of the animal structure, indeed, is a tissue of 

 minute vessels, and the healthful condition of their fluid 

 contents is alone preserved by the vortex-like movements to 

 which they are constantly subjected by muscular fibres and 

 the nerves, so that the life is in the blood as much as in the 

 heart or the brain. The sanguiferous system being but a ra- 

 diation of the digestive throughout the body, they keep 

 pace, and follow the same laws, in the march of their deve- 

 lopment in the animal kingdom as in the embryo. In the 

 embryo, as in the animal kingdom, capillaries precede 

 trunks in the order of formation, as the pulsating vessel 

 precedes and forms the ventricle. The existence of the 



