MAMMARY GLANDS 



73 



the excretion of the mammary glands. The lowest order of 

 mammals, the Monotremata, lay eggs and the young hatch 

 out in a very rudimentary condition. They are at once 



Fig. 23. The Rock Wallaby with young in pouch, Petrogale xanthopus. 



After Vogt and SiJecht. 



