CHAPTER SECOND. 



CHYL1FEROUS SYSTEM. 



THE assimilation of foreign matter to the textures of the 

 body is comparatively a simple process, and effected by the 

 simplest means, in the lowest tribes of animals, where there 

 are few elements in the food, and few in the textures into 

 which it is to be converted ; so that the same alimentary 

 cavities which receive and digest the food, transmit the assi- 

 milated portion through their parietes, to form part of the 

 homogeneous tissue of their body. This low condition of 

 development may exist in the simpler forms of poriphera, 

 polypiphera and acalepha ; but in tracing the progress of the 

 digestive cavity through all its metamorphoses and grades 

 of development in the animal kingdom, we have seen it 

 become more extended and complicated, more finely orga- 

 nized, and divided into distinct parts with distinct functions, 

 as we ascend in the scale; follicles, cceca, tubuli, glands, 

 and vessels, develope from its sides, and become more or 

 less distinct in connection and function ; a sanguiferous 

 system thus becomes isolated and developed, to extend the 

 source of nutriment to each point of the body, and the nu- 

 tritive fluid of this complex hydraulic apparatus, is received 

 from the alimentary canal, directly by the veins, in most of 

 the invertebrated classes. In all the higher animals, how- 

 ever, constituting the vertebrated division, a distinct system 

 of vessels is employed to receive, and still further to elabo- 

 rate, the fluid product of digestion, and to convey it to the 

 venous system. The fluid which these vessels take up from 

 the intestine, being generally opaque and of a whitish colour 

 in quadrupeds, has received the name of chyle or lacteal 

 fluid, and the vessels, plexuses, glands and ducts, through 

 which it passes in its way to the blood, constitute the chyli- 

 ferous system, which like other complex systems, presents 



