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SLOUGHING IN SERPENTS. 

 By Gerald Leighton, M.D. 



The process, common to all reptiles, of periodically casting 

 off a " slough " is a very interesting one to watch, and can best 

 be observed in serpents. It is not often the good fortune of the 

 observer to be able to see it in natural conditions, though I have 

 encountered several Adders engaged in the act ; but in serpents 

 in captivity the whole process can be studied with ease and 

 accuracy. In books which touch on the subject three statements 

 are to be found, which, in my experience, are inaccurate, or at 

 any rate only partially true. It is said, in the first place, that 

 the slough is cast once every year ; secondly, that the reptile 

 often makes a meal of the cast-off slough ; and, thirdly, that the 

 slough is cast entire {i. e. in one piece) when the reptile is in 

 good health, but in several pieces if the animal is out of con- 

 dition. It is quite possible that various species exhibit in- 

 dividual peculiarities in this matter, but in the case of British 

 reptiles none of these statements are quite accurate. In the 

 first place, it is usual for both Adders and Ring- Snakes to cast 

 their sloughs three, four, or even five times in a season. The 

 first sloughing takes place immediately after the winter hiberna- 

 tion is over, and the process is repeated at intervals of six weeks 

 or two months. The same remark applies to the Slowworm 

 {Anguis fragilis). Secondly, I doubt whether any one of the 

 three species mentioned ever swallows the cast-off slough — at 

 any rate, those I have kept have never done so. It is no doubt 

 true that some amphibians do this, and probably this accounts 

 for the idea that serpents act in a similar manner. The third 

 point is perhaps the most interesting, and it is that to which I 

 wish specially to draw attention in this paper. What determines 

 whether the slough comes off whole or in pieces ? To answer 

 this question it is necessary to understand the nature of the 

 process. There are two distinct stages in the act of sloughing* 



