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the performances of all the vital functions, and among 

 others that of growth. Thus it may be that acceleration 

 can be accounted for, and the process of the develop- 

 ment of the orders and sundry lesser groups of the Ver- 

 tebrate kingdom indicated ; for, as already pointed out, 

 the definitions of such are radically placed in the differ- 

 ent structures of the organs which aerate the blood and 

 distribute it to its various destinations. 



But the great question, What determined the direc- 

 tion of this acceleration? remains unanswered. One 

 cannot understand why more highly-oxidized blood 

 should hasten the growth of partition of the ventricle 

 of the heart in the serpent, the more perfectly to sepa- 

 rate the aerated from the impure fluid ; nor can we see 

 why a more perfectly-constructed circulatory system, 

 sending purer blood to the brain, should direct acceler- 

 ated growth to the cerebellum or cerebral hemispheres 

 in the crocodile. 



b. In Characters of the Specific Kind. Some of the 

 characters usually placed in the specific category have 

 been shown to be the same in kind as those of higher 

 categories. The majority are, however, of a different 

 kind, and have been discussed several pages back. 



The cause of the origin of these characters is shrouded 

 in as much mystery as that of those which have occu- 

 pied the pages immediately preceding. As in that case, 

 we have to assume, as Darwin has done, a tendency in 

 Nature to their production. This is what he terms " the 

 principle of variation/' Against an unlimited variation 

 the great law of heredity or atavism has ever been op- 

 posed, as a conservator and multiplier of type. This 

 principle is exemplified in the fact that like produces 

 like that children are like their parents, frequently even 



