ANIMAL ORGANIZATION. 113 



garment ; so that, however firmly a person may 

 attempt to grasp the animal by the neck, it can 

 easily turn its head completely round, and bite the 

 fingers that are holding it. In like manner the 

 skin of the frog is attached to the body only at a 

 few places, and may be readily stripped off. A 

 thin layer of muscular fibres is often found lying 

 immediately underneath the skin, and is provided 

 for the purpose of moving it over the subjacent 

 parts. In animals that roll themselves into a 

 ball, as the hedge-hog, these muscles are of 

 great size and importance. We shall see that 

 in the mollusca, this muscular apparatus is inse- 

 parably blended with the integument, and com- 

 poses a peculiar structure, termed the mantle, 

 Immediately covering the corium is the Rete 

 Mucosum, which is a very thin layer of soft 

 animal matter, composed of a net-work of delicate 

 fibres, and containing more or less of the material 

 from which the colour of the skin is derived, 



The Epidermis is a membrane of a very 

 peculiar nature, consisting of a thin expansion of 

 albuminous matter, apparently homogeneous in 

 its texture and composition. It is impervious to 

 fluids, although capable of imbibing moisture, 

 and of slowly transmitting a portion to the sub- 

 jacent textures. Its thickness varies exceedingly 

 in different parts ; being adapted to the kind of 

 protection it has to afford against pressure, 

 friction, or other causes of injury. As it is not 



VOL. i. I 



