DO SNAKES INCUBATE 'i 433 



the world in the shape of an egg, and its first business is 

 to push through the filmy membrane which envelops it in 

 its imprisoned form.' This is contrary to our accepted ideas, 

 though partially true in this instance. The word viper is 

 generally supposed to be derived from the Latin vipera, a 

 contraction of vivipara, to produce alive. The above words 

 therefore are inapplicable as a rule. 



So far as was known in Aristotle's time, only certain 

 venomous species common in the countries with which 

 classic writers were best acquainted did produce live young, 

 and they were mostly what are still known as * vipers,' a term 

 restricted to these and explained as being derived from 

 such signification. 



Opportunities of study and of observation afforded in 

 menageries and zoological gardens at the present day have 

 caused the term viper d,s relating to gestation to be discarded, 

 or many non-venomous snakes must be included, thus over- 

 throwing all our notions of vipers. As was shown in the pre- 

 ceding chapters, the name is now associated with dentition. 



German and French ophiologists affirm that the three 

 distinctions of oviparous, viviparous, and ovoviviparous are 

 founded on no other ground than the greater or less deve- 

 lopment of the foetus at the time of deposition. 



The nature of the egg-covering or ' shell ' has also to do 

 with this. In eggs which take a longer time to mature or 

 to ' hatch,' the external covering is thicker and more leathery; 

 in those which are hatched either before or on deposition, 

 the shell is thinner, more membranous. Always, however, 

 there is a calcareous element in the shell, and the eggs are 



generally, but 7iot invariably, linked together. 



2 E 



