OVIPAROUS, OVO-VIVIPAROUS AND VIVIPAROUS. 19 
OVIPAROUS, Ovo-VIVIPAROUS AND VIVIPAROUS. 
Some kinds of snakes lay eggs, and others give birth to young. 
Some species 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 which have not 
started incubating are known as oviparous snakes. 
Some snakes lay eggs which have been more or less incubated 
before being laid. In certain cases the young are almost fully 
developed inside the eggs when they are laid. In others there 
are varying stages of 
development of the 
young. These are 
known as ovo-vivipar- 
ous snakes, which 
means ‘“ producing 
eggs which are more 
or less incubated inside 
the parent’s body.”’ 
There are yet other 
snakes which give birth 
to fully developed 
young. In these cases 
the eggs are developed 
full size within the 
Fic. 11.—Night or Demon Adders hatching out. Two 
parent’s body, and they are out, others are seen in the act of breaking the egg 
a ‘ shells. 
incubate there until 
the young are completely developed. They are then born, each 
enveloped separately in a transparent membraneous bag, which 
their active struggling ruptures. Viviparous means giving birth 
to living young. 
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 lies as often as 
possible in the sunshine. In captivity she invariably lies on the 
part of the floor where the sun happens to shine. 
At the Port Elizabeth Museum the sun only shines for an 
