86 INTRODUCTION 



the base of the tail upwards, in order to extend the 

 cloacal opening. The eggs are all produced together, 

 usually at intervals of a few minutes, and generally 

 adhere to one another by means of a sticky fluid 

 secreted by the oviducts, thus forming a clump. 

 In ovoviviparous snakes the young are born in 

 succession, in the course of a few hours or of a few 

 days. In many oviparous species it is the rule for 

 freshly-laid eggs to contain more or less developed 

 embryos, and Coronella punctata is said to produce 

 thin-shelled eggs which hatch in less than half the 

 time required for the eggs of its American congeners 

 under the most favourable circumstances. There is 

 thus almost every degree between oviparity and 

 ovoviviparity. 



These two modes of parturition bear no relation to 

 the natural affinities of snakes. Thus, the European 

 Coronella austriaca is ovoviviparous, and its North 

 American congeners are oviparous ; whilst, curiously, 

 it is the inverse in the genus Tropidonotus. It was long 

 believed to be an invariable rule for the Viperidae to 

 bring forth live young, the name Viper being derived 

 from this well-known peculiarity, but it has now been 

 ascertained that the South American Lachesis mutus, 

 the Indo-Malay Lachesis monticola, and the African 

 Causus and Atractaspis, lay eggs. All exclusively 

 aquatic snakes, such as the Hydrophiinse, are ovovi- 

 viparous, and thus dispensed from going on land for 

 parturition. 



