96 
COMPARATIVE ZOOLOGY. 
The laeteals 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 laeteals 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, 
and in many Vertebrates, as 
Frogs and Fishes, by lymph 
receptaculum chyli. The oval bodies 7 
are glands. hearts. 
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 laeteals is not 
yet well understood, but the laeteals are themselves rhyth¬ 
mically contractile , 63 and force the absorbed chyle tow- 
Fig. 61.—Principal Lymphatics of the Hu¬ 
man Body: a, union of left jugular and 
subclavian veins; b, thoracic duct; c, 
