110 PLAIN FACTS FOR OLD AND YOUNG 



occurred in which a much longer time has been re- 

 quired; and numberless cases are recorded in which 

 human beings have been born several weeks before the 

 expiration of the usual time, as stated. There is some 

 uncertainty respecting the exact length of the period 

 of gestation, which grows out of the difficulty of deter- 

 mining, in many cases, the exact time when conception 

 took place. 



In the kangaroo, though the period required for de- 

 velopment is about the same as in the human female, 

 uterine gestation continues for only thirty-nine days. 

 At the end of this time, the infant kangaroo is trans- 

 ferred to a pouch provided under the hinder part of 

 the body of the mother, which also contains the mam- 

 mary glands. To the nipple of one of these, the lips of 

 the young animal become attached, and by a curious 

 rhythmical action of certain muscles, the paternal nour- 

 ishment is regularly forced into the mouth of the little 

 one. The eminent Professor Owen thus remarks con- 

 cerning this remarkable mode of caring for the young : 



''Thus aided and protected by modifications of 

 structure, both in the system of the mother and in its 

 own, designed with special reference to each other's 

 peculiar condition, and affording, therefore, the most 

 irrefragible evidence of creative foresight, the feeble 

 offspring continues to increase from sustenance derived 

 exclusively from the mother, for a period of about 

 eight months. The young kangaroo may then fre- 

 quently be seen to protrude its head from the mouth 

 of the pouch, and to crop the grass at the same time 

 the mother is browsing. Having thus acquired addi- 

 tional strength, it quits the pouch, and hops at first 

 with a feeble and vacillating gait, but continues to re- 

 turn to the pouch for occasional shelter and sujjplies of 



