THE SKIN AND SKELETON. 125 
well-developed glands, two in number, and consisting of 
closely packed tubes. 
3. The skin of the soft-skinned animals, particularly 
of Amphibians and Mammals, are covered with minute 
pores, which are the ends of as many delicate tubes that 
lie coiled up into a knot within the true skin. These are 
the sweat-glands, which excrete watery vapor, and with it 
certain salts and gases. The importance of this excretion, 
known as perspiration, is shown by the fact that if the 
skin be varnished over, the animal will die. On the ac- ' 
cession of Leo X. to the papal chair, a child was gilded 
all over, at Florence, to represent the Golden Age, and it 
died in a few hours. 
Besides these secretions and excretions, there are oth- 
ers, confined to particular animals, and designed for spe- 
cial purposes: such are the oily matters secreted from the 
skin of qnadrupeds for lubricating the hair and keeping 
the skin flexible; the tears of Reptiles, Birds, and Mam- 
mals; the milk of Mammals; the ink of the Cuttle-fish ; 
the poison in the stings of Jelly-fishes and Insects; and 
the silk of Spiders and Caterpillars. 
CHAPTER XVI. 
THE SKIN AND SKELETON. 
The Skin, or Integument, is that layer of tissue which 
covers the outer surface of the body. The term Skeleton 
is applied to the hard parts of the body, whether external 
or internal, which serve as a frame-work or protection to 
the softer organs, and afford points of attachment to mus- 
cles. If external, as the crust of the Lobster, it is called 
Hzxoskeleton ; if internal, as the bones of Man, it is called 
