70 BRITISH SERPENTS. 



the skin is in an unhealthy condition, the snake has 

 more difficulty, or makes no effort, and the cuticle 

 comes off in pieces." 1 This supposition that the health 

 of the serpent is the determining factor in the slough 

 coming off whole or in pieces seems to have become 

 widely believed ; at any rate, I have often heard 

 it mentioned in conversation. But Miss Hopley's 

 favourite ophidian is the ring snake, about which 

 she has written so much and so delightfully, and 

 she seems to have had this species in her mind when 

 writing the above-quoted sentence. At any rate, I 

 have not found it to be the case in adders, unless the 

 adder population of Herefordshire and Monmouth- 

 shire is assumed to contain a very large proportion 

 of invalids, which is hardly likely to be the case, con- 

 sidering the large size they grow to in these counties. 

 My experience with adders is that the slough is more 

 often cast in pieces than whole. The whole process 

 resolves itself into two distinct phases — first, the 

 separating of the external cuticle from the under- 

 lying skin ; and second, the dropping or leaving 

 behind of the portion to be cast off. The first is a 

 physiological process, explained before ; the second is 

 a mechanical process, dependent on external circum- 

 stances, over which the snake may have no control. 

 I regard it as almost accidental, when the slough once 

 is loosened from the body, whether it comes off whole 

 or in separate pieces. In other words, it all depends 



1 British Reptiles, p. 27. 



