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 branchiae or a series of 

 laminse, between which water passes. 



In all the vertebrata, the blood which furnishes the liver 

 with the materials of the bile is venous bloody which has cir- 

 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 urine, 

 which is produced in two large glands, attached to the sides 

 of the spine of the back, called kidyieys 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. 



