68 REPTILES 



correlated with some special feature in the life-history of the 

 species in which they occur, and are therefore mainly, if not 

 entirely, adaptive, although in most instances the reason for 

 such adaptation is not apparent. In the case of the sea-snakes 

 {Hydrophiince), however, which are viviparous, the reason for 

 the departure from the normal oviparous mode of reproduction 

 is plain, as these reptiles, unlike turtles, never voluntarily come 

 to land. The burrowing snakes of the families Illysiidce and 

 Uropeltidce, and possibly also the Typhlopidce, are likewise vivi- 

 parous ; and here again the reason for the specialisation is not 

 very difficult to discover. On the other hand, it is not easy to 

 see why the viper (like most of its tribe) should be viviparous, 

 while the ring-snake is- oviparous. 



Till a few years ago most of the viper tribe were believed to 

 produce their young alive ; that is to say, the eggs are hatched 

 within the body of the female parent, so that, strictly speaking, 

 these reptiles should be described as ovo-viviparous rather 

 than viviparous. In the Field of January I, 1910, there 

 appeared, however, a letter from Mr. C. Leigh in which it is 

 stated that the Himalayan pit-viper {Lachesis monticold) is ovi- 

 parous. This viper, which ranges from the Eastern Himalaya 

 to the Malay countries, is remarkable for the great thickness of 

 its body as compared with the length ; for while it usually 

 attains a length of about 2\ feet, its girth is sufficient for that 

 of an average 5 -foot snake. The ground-colour of the back is 

 ashy-grey, upon which is a series of more or less regular dark 

 blotches, with a sprinkling of black and traces of yellow. On 

 the under-parts the general colour is likewise ashy, but with 

 dark red mottlings. In some examples the dark markings on 

 the upper surface are so pronounced that the reptile is scarcely 

 distinguishable from the freshly-turned black soil of the tea- 

 gardens, in which it is frequently found. It was while working 

 in a garden at Kurseong, during the summer of 1909, that a 

 coolie came across a cluster of snake's eggs. On reaching out 

 his hoe to investigate and pushing the grass aside, he discovered 

 a viper of this species which made a snap at him, but was eventu- 

 ally secured. The tropical American bushmaster {Lachesis 

 inula), and all the members of the African genus Atractaspis 

 are also oviparous. 



An analogous instance is offered by the family Boiidce, in 



