20 



INTEODUCTION. 



calculated for this end is evident to me from the fact established 

 by Dr. Braun that the casting of the shells of river Oray-fish 

 is induced in exactly the same manner by the formation of a 

 coating of hairs which mechanically loosens the old skin or 



Fig. 8.— Casting process in the skin of reptiles, a, in the clinging bristles o£ the foot 

 of the Gecko ; within the epidermis are seen the casting hairs, hh, destined to form 

 the new clinging bristles, h, in the Adder ; hh, the casting hairs ; the portion of skin 

 above them is pushed away, and the haiis themselves form the ridges on the new skin, 

 c, a scale of PhyllodactylJis, with the little sensitive hairs sh at the right edge, rf, T/uca- 

 dacfylm ; 5A, the sensitive hairs ; and hh, the casting hairs which do not change 

 during casting. From Cartier. 



shell from the new. Now the investigations of Braun and 

 Cartier have shown that these casting hairs — which seive the 

 same purpose in two groups of animals so far apart in the 

 systematic scale — after the casting are partly transformed into 

 the concentric stripes, sharp spikes, ridges, or warts which 



