OVIPAROUS AND OVO-VIVIPAROUS. 



19 



Oviparous and Ovo-Viviparous. 



Some kinds of snakes lay eggs, which are quite fresh and are 

 hatched or incubated outside the body, usually by the heat 

 generated by their surroundings, such as decaying vegetation, 

 manure, or the sun-heated ground. Certain snakes are believed 

 to coil round their eggs and incubate them, but this is uncertain, 

 except in the case of the' Python. * Those snakes which lay eggs 

 are known as oviparous snakes. 



In some snakes, such as the Schaapsteker and Night Adder, 

 the eggs are incubated to a certain degree in the parent's body 

 before they are brought forth. 



There are other 

 snakes which give birth 

 to fully developed 

 young. In these cases 

 the eggs are developed 

 full size within the 

 parent'sbody, and they 

 incubate there until 

 the young are com- 

 pletely developed. 

 They are then born, 

 each enveloped separ- 

 ately in a transparent 

 membraneous bag, 

 which their active 

 struggling ruptures. 

 There is no albumen 



surrounding the yolk. The yolk entirely fills the shell. Snakes 

 begin to breed when about 4 years of age. The number of eggs 

 or young depends on the age and size of the parent. These are 

 ovo-viviparous snakes. 



The temperature of a gravid snake is slightly increased, 

 otherwise the embryos or foetal young would not develop satis- 

 factorily. In the wild state the gravid female hes as oft«n as 

 possible in the sunshine. In captivity she invariably lies on the 

 part of the floor where the sun happens to shine. 



* The only other I have observed doing so is the spotted or Rhombic 

 Schaapsteker. 



Fig. 12. — Night or Demon Adders hatching out. Two 

 are out, others are seen in the act of breaking the egg 

 shells. 



