58 
CILIA.—FAT CELLS. 
Tadpole or larva of the Water Newt, which hang down as fringes 
on either side of the neck. In the higher air-breathing 
animals, the function of the cilia is much more limited. They 
clothe the mucous membrane which lines the air-passages; 
and their function appears to he, in that and other cases, to 
prevent the accumulation of the secretion with which the 
membrane is kept moist, by keeping up a continual onward 
- movement of it towards the outlet of the passage. In some 
other cases, however, we find the ducts of secreting organs 
furnished with cilia, whose action is obviously to assist in 
carrying the products of secretion towards their outlet. 
46. Passing on, now, to those tissues of animals of which 
cells constitute the permanent components, instead of being 
successively thrown .off and replaced as they are in the 
Epidermis and Epithelium, we may first notice the Adipose 
tissue, or Fat , in which the oily and fatty matters of the body 
are for the most part contained. This tissue is composed of 
minute cells or vesicles (fig. 14), having no communication 
with each other, but lying side by side in the meshes of the 
areolar tissue, which serves 
to hold them together, and 
through which also the blood¬ 
vessels find their way to 
them. From the fluid in these 
vessels, the fatty matter is 
separated in the first place by 
the secreting action of the 
cells; and it is prevented 
from making its way through 
the very thin walls of the 
cells, by the simple expedient of keeping these constantly 
moist with a watery fluid, the blood. 1 The blood-vessels 
have also the power of taking back the fatty matter again 
into the circulation, when it is wanted for other purposes in 
the economy. These deposits of fatty matter answer several 
important objects. They often assist the action of moving 
parts, by giving them support without interfering with their 
free motions j thus the eye rests on a sort of cushion of fat, 
on which it can freely turn, and through which the muscles 
1 Thus oil will nob pass into blotting-paper, if this have been 
previously moistened with water. 
