260 THE ZOOLOGIST. 



It is a significant fact that a considerable amount of variety 

 is displayed in the form of these excrescences, and that among 

 the individuals of one species this characteristic sign is not 

 constant in size, that of ammodytes, for instance, being often 

 no larger than that of V. aspis. It may be asked how the 

 acquisition of the slight nasal projection in this last named — 

 which looks like a transitional stage — can be of any value to its 

 possessor. 



But this reminds me of the gradations in the means of 

 warning by sound exhibited by various snakes, which are 

 referred to in Darwin's " Expression of the Emotions," * whence 

 we may gather that so unpromising an object as the slightly 

 indurated tail- tips of our European vipers may be the foundation 

 of an organ as highly developed as that of the Eattle snake. 



It would be interesting similarly to follow up tbe various 

 minute steps by which an apparatus so perfected as the poison- 

 glands has been formed. But the greater the specialization — 

 i. e. divergence in one direction — the rarer are the connecting 

 links. Still we find here, as everywhere, various degrees of 

 perfection, though it has become difficult to trace how the 

 venomous saliva has been gradually accumulated, intensified, 

 and collocated into its convenient receptacle. Dr. Leydig relates 

 how on exhibiting a Coronella Icevis to some students at Tubingen, 

 the animal inflicted a bite on his wrist, which caused his whole 

 arm to swell up for some days. In this he recognised the possible 

 commencement of the development of these organs : a concession 

 for so staunch an adherent of the immutability of species. 



But it is still more curious to see how, while some species 

 are improving this chance of success by increased swiftness or 

 by various methods of protective coloration, others — locally 

 separated and working independently, as it were — have dis- 

 covered the identical, and not the least peculiar, of the many 

 contrivances to prolong specific existence. 



;: ' Darwinism,' p. 109 seq. 



