20 



INTRODUCTION. 



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

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

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

 coating of hairs which mechanically loosens the old skin or 



FlG. 8. Casting process in the sMn of reptiles, a, in the clinging bristles of the foot 

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

 the new clinging bristles. 6, in the Adder ; hh, the casting hairs ; the portion of skin 

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

 c, a scale of Phyliodactybis, with the little sensitive hairs s/i at the right edge. <i, Tluca- 

 ciactylus ; fh, 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 se;ve 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 



