96 



COMPARATIVE ZOOLOGY. 



The- lacteals are only a special part of the great lym- 

 phatic system, which absorbs and carries to the thoracic 



duct matter from all parts 

 of the body. 62 The lymph 

 is a transparent fluid having 

 many white blood corpus- 

 cles. It is, in fact, blood, 

 minus the red corpuscles, 

 while chyle is the same fluid 

 rendered milky by numer- 

 ous fat - globules. During 

 the intervals of digestion, 

 the lacteals carry ordinary 

 lymph. This fluid is the 

 overflow of the blood the 

 plasma and white corpus- 

 cles which escape from the 

 blood capillaries, and are not 

 needed by the tissues in 

 which they are. This sur- 

 plus overflow is returned to 

 the blood by the lymphatics. 

 The current is kept up by 

 the movements of the body, 

 an( j j n mariy Vertebrates, as 



FIG. 61. Principal Lymphatics of the Un- 

 man Body: a, union of left jugular and 

 subclavian veins; &, thoracic duct; c, Fl'OgS and FisllCS, by lymph 



hearts. 



The oval bodies 



receptaculum chyli 

 are glands. 



Like the roots of Plants, the absorbent vessels do not 

 commence with open mouths; but the fluid which enters 

 them must traverse the membrane which covers their mi- 

 nute extremities. This membrane is, however, porous, 

 and the fluids pass through it by the forces of filtration 

 and diffusion. How the fat gets into the lacteals is not 

 yet well understood, but the lacteals are themselves rhyth- 

 mically contractile, 68 and force the absorbed chyle tow- 



