THE CONQUEST OF THE 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 



