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THE AMERICAN NATURALIST. [Vol. XXXVII. 



erally, one less vertebra in man than in the still arboreal apes. 

 On the other hand among the marsupials where typically arbo- 

 real forms prevail the number is constant for the group — nine- 

 teen. This may be clue to the fact as Dollo has shown that the 

 terrestrial forms have but very lately modified themselves to this 

 mode of life — the whole group of marsupials having been at one 

 time arboreal. In like manner the number in the carnivores is 



Among isolated adaptations mav be mentioned the modified 



As described by Dobson 



