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 be, 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 ; 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. 



Fig. 14. FAT CELLS, HIGHLY 



MAGNIFIED. 



