TEGUMENTS OP EEPTlLESc 55.3 



a glandular fold curves from above the tympanum to the axilla or 

 shoulder. 



The skin takes an important share in respiration in the 

 Anourous Batrachia,' and there is a relation of ' supply and 

 demand ' Ijctween the cutaneous follicles and the large allantoic 

 liladder : the latter would seem to receive water directly by the 

 cloaca, when the Frog may be in that element, and to serve as a 

 reservoir for the supply of cutaneous transpiration when the 

 batrachian is on dry land.^ 



The cpiderm is periodically shed in Butrachia. It comes away 

 in shreds in the aquatic kinds. In the Toad the old epiiderm 

 sjdits along the middle line of both back and belly, and each 

 lateral half is wriggled off in folds towards the sides. It is then, 

 l)y contortions of the trunk and limbs, loosened from the hind- 

 limbs, and removed from them by the animal bringing first one and 

 then the other leg forward under the arm, when, by withdrawing 

 the hind-leg, its cuticle is left under the fore-leg. The two 

 jiortions are now pushed forward to the mouth, by the help of 

 which the anterior extremities are also divested of their cuticle. 

 The whole mass is finally pushed by the hands into the mouth, 

 and swallowed at a single gulp. The new cuticle is bright, soft, 

 and covered with a colourless niucus.^ 



In Serpents the epiderm is shed, usually entire, and the animal, 

 ]>artially blindfolded hj the opacity of the layer passing over the 

 cornea, fig. 220, c, seeks an obscure retreat ; but I have watched 

 the process of exuviation in a captive snake. It rubs the front 

 and sides of the mouth against its prison wall, thus detaching and 

 reflecting the cuticle from the oral margin, until it is turned back 

 from over the whole head : the snake then brings forward its tail 

 and coils it transversely round the head, and by pushing the head 

 through the coil turns the cuticle back upon the neck ; then 

 tightening the coil and renewing the forward movement, threading 

 the body, as it were, through the caudal ring, the cuticle is 

 jtushed further and further back until the eversion has been 

 carried so near the end of the tail as prevents the further action 

 of the coil; the animal finally glides along dragging behind the 

 whole of the loosened epiderm, and a few wriggling actions of the 

 tail serve to completely detach it. Thus, the entire outer skin of 

 the snake may be found shed and turned inside out, the process of 

 exuviation being like the turning off a stocking from the leg and 

 foot. The Avhole of the exuviable epiderm in Ophidia has l^een 

 condensed into the form of scales : these are small and pretty 

 ' ccxcvn. ° lb. ' ccxcviii. vol i. p. 102. 



