94 
COMPARATIVE ZOOLOGY. 
stood. It emulsifies and saponifies, part of the fats, so that 
they are dissolved, and perhaps aids in preventing the food 
from decomposing during the process of digestion and ab¬ 
sorption. The chyle is slowly driven through the small 
intestine by the creeping, peristaltic motion of its walls, 60 
the nutritious portion being taken up by the absorbents, 
as described in the next chapter, while the undigested part 
remaining is discharged from the large intestine. 61 
CHAPTER XI. 
THE ABSORBENT SYSTEM. 
The nutritive matter (chyle), prepared by the digestive 
process, is still outside of the organism. How shall it 
enter the living tissue? 
In animals, like the Infusoria and Polyps, whose digest¬ 
ive department is not separated from the body-cavity, the 
food, as soon as dissolved, mingles freely with the tissues 
and organs it has to nourish. In the higher Invertebrates 
having an alimentary canal, the chyle passes, by simple 
transudation, through the walls of the canal directly into 
the soft tissues, as in Insects, or is .absorbed from the canal 
by veins in contact with it, as in Sea-urchins, Mollusks, 
Worms, and Crustaceans, and then distributed through 
the body. 
In Vertebrates only do we find a special absorbent sys¬ 
tem. Three sets of vessels are concerned in the general 
process by which fresh material is taken up and added to 
the blood: Capillaries, Lacteals, and Lymphatics. 
Only the tw T o former draw material from the alimentary 
canal. 
It is a general law that the food is absorbed as fast as 
