THE BREEDING BEHAVIOR OF ANIMALS 



189 



Eggs thus carried in pouches may perhaps receive oxygen from the parent, 

 but little is known on this subject. Either the male or female may carry 

 the eggs, but usually only one sex does this in any given species. 



Care of the Young after Birth or Hatching: Birth Stages. — After 

 birth in viviparous forms and after hatching in oviparous species, the 



Fig. 160. — The black swamp wallaby. The young are born in a very immature stage 

 and are carried in a pouch (marsupium) on the ventral side of the mother. {Photograph 

 loaned by the New York Zoological Society.) 



young may or may not require protection and assistance in getting 

 food. This is partly dependent upon the stage of development which the 

 offspring has attained at the time of birth, but not entirely so. 



The animal may leave the egg complete in all its parts and needing 

 only the growth of the body and the maturity of the sex cells to attain 

 the climax of its development. Among these forms the young may 



