THE SHEDDING OF THE SKIN. 83 



hai'dens. This sort of moulting is -what is technically' 

 termed ecdysis, or exuviation. It is commonly spoken of 

 as the " shedding of the skin," and there is no harm in 

 ii>5ing this phrase, if we recollect that the shed coat is not 

 the skin, in the proper sense of the word, but only what 

 is termed a cuticular layer, which is secreted upon the 

 outer surface of the true integument. The cuticular 

 skeleton of the crayfish, in fact, is not even so much a 

 part of the skin as the cast of a snake, or as our own nails. 

 For these are composed of coherent, formed parts of the 

 epidermis ; while the hard investment of the crayfish con- 

 tains no such formed parts, and is developed on the out- 

 side of those structures which answer to the constituents 

 of the epidermis in the higher animals. Thus the cray- 

 fish grows, as it were, by starts ; its dimensions remaining 

 stationary in the intervals of its moults, and then rapidly 

 increasing for a few days, while the new exoskeleton is 

 in the course of formation. 



The ecdysis of the crayfish was first thoroughly 

 studied a century and a half ago, by one of the most 

 accurate observers who ever lived, the famous Reaumur, 

 and the following account of this very curious process is 

 given pearly in his words.* 



A few hours before the process of exuviation com- 



■* See Reaumur's two Memoirs, " Sur les diverses reproductions qui 

 Be font dans les eprevisses, les omars, les crabea, etc.," " Histoire de 

 rAoademie royale des Sciences," annee 1712 ; and "Additions aux ob- 

 servations sur la mue des ^orevissea donnees dans les Memoires de 1712." 

 Ibid. 1718. 



