102 THE MECHANICAL FUNCTIONS. 



sist of a supply of oily fluid, prepared in small 

 cavities wliich are situated in the skin itself, and 

 have minute ducts opening upon the surface. These 

 cavities, termed sebaceous follicles, are generally 

 interspersed in great numbers in different parts of 

 the body, abounding more especially in those 

 places where folds occur, and where there is the 

 greatest friction. In Fishes, Mollusca, and other 

 aquatic animals, the skin is at all times defended 

 from the action of the water by a viscid or glu- 

 tinous secretion, prepared in this manner, and con- 

 tinually poured out on the surface, through ducts, 

 the orifices of which are easily seen with the 

 naked eye, disposed in a line on each side of the 

 body. 



The Chameleon has long been celebrated for the 

 changes of colour it exhibits at diflterent times, and 

 which credulous observers asserted the animal could 

 effect at pleasure, so as to assume that of adjoining 

 objects. It is, however, an undoubted fact that 

 frequent and remarkable changes of colour take 

 place in the skin, from causes not easily determin- 

 able ; and which has been attempted to be explained 

 on different hypotheses more or less plausible, but 

 in reality devoid of all foundation in truth. But 

 the recent and accurate researches of Milne Ed- 

 wards appear at length to have solved tlie enigma, 

 by the discovery of a curious apparatus of follicles, 

 or minute bladders, arranged in a layer underneath 

 the true skin, and containing a fluid pigment, of 

 a dark bottle-green colour. From the outer end 

 of each of these follicles, there proceed several 

 tubes, which divide and ramify into very minute 

 branches rising towards the epidermis, and pene- 



