VERTEBRATES: BACKBONE AND BRAIN 87 



vive to bear witness of these old oviparous groups, and 

 these only iu New Zealand. These retain several old 



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reptilian characteristics. Their lower position is shown 

 also by the fact that the temperature of their bodies is, 

 at least, ten degrees Fahrenheit below that of higher 

 mammals. One of these carries the egg in a pouch on 

 the ventral surface ; the other, living largely in water, 

 deposits its eggs in a nest in a burrow in the side of 

 the bank of the stream. 



After these came the marsupials. In these the eggs 

 develop in a sort of uterus ; but there is no placenta, 

 in the sense of an organic connection between the em- 

 bryo and the uterus of the mother. The young are at 

 birth exceedingly small and feeble. The adult giant 

 Kangaroo weighs over one hundred pounds ; the young 

 are at birth not as large as your thumb. They are 

 placed by the mother in a marsupial pouch on her 

 ventral surface, and here nourished till able to care for 

 themselves. 



Pardon a moment's digression. The marsupials, ex- 

 cept the opossum, are confined to Australia, and the 

 oviparous mammals, or monotremes, to New Zealand. 

 Formerly the marsupials, at least, ranged all over 

 Europe and Asia, for we have indisputable evidence in 

 their fossil remains. But they have survived only in 

 this isolated area, and here apparently only because 

 their isolation preserved them from the competition 

 with higher forms. If the Australian continent had 

 not been thus early cut off from all the rest of the 

 world, the only trace of both these lower groups would 

 have been the opossum in America and certain pe- 

 culiarities in the development of the egg in higher 

 mammals. This shows us how much weight should be 



