HIBERNATION. 43 
SALT-WATER SNAKES. 
These snakes inhabit the ocean, and feed upon fish and other 
marine creatures. They are all very venomous. These Salt- 
water Snakes are distinguished from all other snakes in having a 
keel-like tail, flattened at the sides, which they use as a propeller. 
They possess no fins and are true snakes, and therefore real sea 
serpents. As far as is known, they are all viviparous. The 
gravid female visits the shallow waters of rocky coasts and 
gives birth to her young in the rock pools. Sea snakes are usually 
brilliantly coloured. They are seldom found in mid-ocean. 
MIGRATION. 
Snakes do not migrate from one locality to another, unless 
forced by hunger or a change in their surroundings, such as an 
unusually heavy rainfall, rendering the ground more or less 
marshy, or the slow change brought about by the prolonged 
droughts which occur from time to time in various districts. 
They always remain in the same locality as long as food is pro- 
curable. Most species have some favourite spot to which they 
retire when desiring to rest, or to escape from their enemies. 
. HIBERNATION. 
Snakes usually hibernate during the colder months of each 
year. They do this for two good reasons. Food is scarce during 
the winter months. Snakes are largely dependent for their 
vitality on the temperature of the surrounding air, their bodies 
being unable to accommodate themselves to rapid changes of 
temperature owing to the very slow circulation of their blood 
and consequent low normal temperature. In the tropics and in 
favourable situations in temperate climates, snakes often remain 
active all the year round. In certain localities in South Africa 
several species of snakes do not hibernate. Others hibernate 
only when the days are very chilly, but if a warm breeze should 
blow, and the temperature of the air rises a few degrees, they 
will often issue out of their lurking places to bask in the sunshine. 
I have examined snakes quite stiff and rigid, and apparently dead 
