ANIMALIA VERTEBRATA. 35 
two principal ones are the juices of the gland called the pan- 
creas, and bile, a product of another very large gland named 
the liver. 
While the digested aliment is traversing its canal, that por- 
tion of it which is fitted for nutrition, called the chyle, is ab- 
sorbed by particular vessels styled lacteals, and carried into 
the veins; the residue of the nourishment of the parts is also 
carried into the veins by vessels analogous to these lacteals, 
and forming with them one same system called the lymphatic 
system. 
The blood which has served to nourish the parts, and which 
has just been renewed by the chyle and lymph, is returned to— 
the heart by the veins—but this blood is obliged, either 
wholly or in part, to pass into the organ of respiration, in or- 
der to regain its arterial nature, previous to being again sent 
through the system by the arteries. In the three first classes 
this respiratory organ consists of lungs, that is, a collection of 
cells into which air penetrates. In fish only, and in some 
reptiles, while young, it consists of branchie or a series of 
lamin, between which water passes. 
In all the vertebrata, the blood which furnishes the liver 
with the materials of the bile is venous blood, which has eir- 
culated partly in the parietes of the intestines, and partly in 
a peculiar body called the spleen, and which, after being 
united in a trunk called the vena porta, is again subdivided 
at the liver. 
All these animals have a particular secretion; the wine, 
which is produced in two large glands, attached to the sides 
of the spine of the back, called Azdneys—the liquid they 
secrete is most commonly poured into a reservoir, named 
bladder. 
_ The sexes are separate, and the female has always one or 
two ovaries, from which the eggs are detached at the instant 
of conception. ‘The male fecundifies them with the seminal 
_ fluid, but the mode varies greatly. In most of the genera of 
the three first classes, it requires an intromission of the fluid ; 
in some reptiles, and in most of the fishes, it takes place after 
the exit of the egg. 
