184 



OEGANS OF DIGESTION. 



digestion is not further modified by respiration, but circulates 

 through the body as chyle. 



Tig. 187. 



Fig. 188. 



13 



333. The chyle is composed of minute, colourless glo- 

 bules, of a somewhat flattened form. In the vertebrata, it is 

 taken up and carried into the blood by means of very minute 

 vessels, called lymphatic vessels or lacteals,w}iich are distributed 

 everywhere in the walls of the intestine, and communicate with 

 the veins, forming also in their course several glandular 

 masses, as seen on a portion of intestine connected with a vein 

 (fig. 189), and it is not until thus taken up and mingled with 

 the circulating blood that any of our food really becomes a 

 part of the living body. Thus freed of the nutritive portion 

 of the food, the residue of the product of digestion passes on 

 to the large intestine, from whence it is expelled in the form 

 of excrement. 



334. The organs above described constitute the most es- 

 sential for the process of digestion, and are found more or less 

 developed in all but some of the radiated animals ; but there 

 are, in the higher animals, several additional ones for aiding in 

 the reduction of the food to chyme and chyle, which render 

 their digestive apparatus quite complicated. In the first place, 

 hard parts, of a horny or bony texture, are usually placed about 



