THE CONQUEST UF ‘LHt DRY LAND 209 
Except in the case of some sprawling crea- 
tures, like centipedes and snakes, the body of 
a land animal tends to be compact. The 
weight has usually to be lifted and supported 
off the ground, whereas in an aquatic animal 
the weight is supported in the water. An 
animal like a jelly-fish is unthinkable on land. 
NEW WAYS OF LOOKING AFTER THE 
YOUNG 
The conquest of the land necessarily means 
new ways of looking after the eggs or the 
offspring. For the aquatic animal, it is often 
enough simply to liberate the eggs into the 
water, which serves as their soft cradle; but it 
would be fatal in most cases if a land animal 
merely laid its eggs or its young ones on the 
ground. They would be dried up or de- 
voured. So we find many ways in which 
safety is secured, e.g. by burying the eggs in 
underground nests; or by keeping the young 
ones within the mother’s body for a long time 
before birth, so that they are not very helpless 
when born; or by carrying them about after 
birth, as in kangaroos and opossums. 
One of the ways of securing the safety of 
