262 HAEIT AND INTELLIGENCE. [cHAP. 



Characters lopment of any organism goes on, it acquires first the 

 widest characters belonging to the widest group in which it can 

 group he classed, and afterwards acquires the characters of suc- 

 first!^^ cessively narrower and narrower groups. This is known 

 Von Bar's as Von Bar's law. Stated in these general terms, it will 

 law. perhaps be scarcely intelligible, but an example will make 



it easily understood. Were it possible to watch the de- 

 velopment of a chicken as it actually goes on in the egg, 

 we should see it first acquire those characters which it 

 has in common with all other Vertebrata ;^ and it would 

 be capable of being identified as a vertebrate embryo, 

 before it could be known to which class of oviparous Verte- 

 brata it belonged. It would next be seen to acquire the 

 characters of a bird, without anything to enable us to 

 say what kind of bird ; afterwards it would acquire the 

 characters of the gallinaceous family of birds, and after 

 that, those of the domestic fowl ; last of all, the characters 

 that distinguish the variety or breed. And this differen- 

 tiating process does not stop at birth, for young animals 

 belonging to different breeds of the same species, or to 

 diiferent species of the same genus, are generally — indeed 

 almost invariably — more nearly alike than are the mature 

 animals. 



The characters of the widest group appear first — or, 

 what means the same, the characters that appear first are 

 those which the species has in common with the greatest 

 number of others ; and those which appear last are the 

 peculiar characters of the species — or, in variable species, 

 the peculiar characters of the variety or of the individual. 

 This is the statement of Von Bar's great and simple law. 



1 "In my possession are two little embryos in spirit, whose names I 

 have omitted to attach, and at present I am quite unable to say to what 

 class they belong. They may be lizards, or small birds, or very young 

 mammalia, so complete is the similarity in the mode of formation of the 

 head and trunk in these animals. The extremities, however, are still 

 absent in these embryos. But even if they had existed in the earliest 

 stage of their development, we should learn nothing ; for the feet of 

 lizards and mammals, the wings and feet of birds, no less than the hands 

 and feet of man, all arise from the same fundamental form." (Von Bar, 

 quoted in Darwin's Origin of Species, p. 519.) 



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