EARLY DAYS AND EARLY WAYS 7 



affords a by no means common standard of measurement. 

 There is a by no means sharp division between the embry- 

 onic and post-embryonic stages of development : nor do 

 the post-embryonic stages of development even in closely 

 related animals follow similar lines. 



The platypus and the echidna afford illustrations of 

 these facts. In the former the egg when laid is deposited 

 in a nest in a burrow, and brooded, bird-wise ; in the 

 echidna the egg as soon as laid is thrust by the parent's 

 beak-Hke muzzle into a pouch on the belly answering to 

 that of the kangaroo. Here it is carried until the young 

 hatches, when the shell is thrown out and the young 

 settles down to grow. The platypus has no pouch. 



The marsupials — among which the kangaroos are 

 familiar forms — represent a grade higher in the evo- 

 lutionary scale. Here the young are born. That is to 

 say the egg, as in the case of all the rest of the mammals, 

 no longer becomes enclosed within a shell containing a 

 store of food material for the nourishment of the growing 

 embryo, but instead becomes attached to the wall of the 

 uterus or womb, and draws its nourishment from the 

 maternal tissues. Sooner or later the development of 

 the embryo runs its appointed course and birth takes 

 place. Now in the kangaroo this occurs when the young 

 is but ill formed, minute, blind, naked, and helpless. 

 It is then transferred by the parent, by means of her 

 lips, to her pouch, there to slowly acquire consciousness 

 and activity. But mark the difference between this 

 sojourn in the maternal pouch in the case of the kangaroo 

 and the echidna. ■ In the latter the nourishing milk 

 appears as an exudation from the skin, and is lapped up 

 by the young : the same applies in the case of the platypus. 

 But in the kangaroo this wasteful and primitive arrange- 



