AND DESERTS 137 



In one respect, however, the kangaroo shows a very 

 striking contrast to the ungulates. We have noted 

 that among the swift ungulates the tendency is for the 

 young to be born very fully developed, able after a very 

 short period to run by the side of the parent. The 

 consequent long period of gestation is dangerous to 

 the mother, but has apparently been justified in the 

 struggle for existence by the higher survival rate of 

 the young. Further, as we may note readily among 

 domesticated sheep, the young imgulate, when suck- 

 ling, is not allowed by the mother to satisfy its appetite 

 completely — ^it must never be so satiated as to be in- 

 capable of flight. In the case of the kangaroo con- 

 ditions are very different. The period of gestation is 

 very short, and the young one is bom in a very im- 

 perfectly developed condition, incapable of sucking and 

 quite incapable of voluntary movement. It is placed 

 by the mother in the pouch with which she is provided, 

 and attached to the teat. Milk is then pumped into 

 its mouth, by the action of certain of the muscles of 

 the mother. Owing to this abundant food, growth is 

 rapid, and soon the young one is able to move and 

 leave the pouch. It however always returns to it 

 on an alaim, and is not able to care for itself 

 till it is some eight or nine months old. The mother 

 shows great devotion to her young, but if hard pressed 

 by dogs she wiU throw the young one out of the 

 pouch into the fern, thus reheviag herself of a weight 

 which diminishes her speed. The action has been 

 variously interpreted. According to some authorities 

 the chances are that the dogs -will neglect the young 

 one and continue to chase the mother, who, if she 

 escapes, wiU return to pick up her ' joey '. Others 

 regard the action as equivalent to an abandonment of 



