DARWIN ON MORPHOLOGY 233 



the second with the general evidence for evolution. It is in 

 the second part that the paragraphs on morphological matters 

 occur. In paragraph 7, on affinities and classification, 

 Darwin points out that on the theory of evolution homological 

 relationship would be real relationship, and the natural 

 system would really be genealogical. In the next paragraph 

 he notes that evolution would account for the unity of type 

 in the great classes, for the metamorphosis of organs, and for 

 the close resemblance which early embryos show to one 

 another. It is of special interest to note that he definitely 

 rejects the Meckel-Serres theory of recapitulation. " It is 

 not true," he writes, " that one passes through the form of 

 a lower group, though no doubt fish more nearly related to 

 fcetal state" (p. 42). The greater divergence which adults 

 show seems to him to be due to the fact that selection acts 

 more on the later than on the embryonic stages. He realises 

 very clearly how illuminative the theory of evolution is when 

 applied to the puzzling facts of embryonic development. 

 ' The less differences of fcetus this has obvious meaning on 

 this view: otherwise how strange that a horse, a man, a bat 

 should at one time of life have arteries, running in a manner 

 which is only intelligibly useful in a fish ! The natural system 

 being on theory genealogical, we can at once see why foetus, 

 retaining traces of the ancestral form, is of the highest value 

 in classification " (p. 45). 



Abortive organs, too, gain significance on the evolutionary 

 hypothesis. "The affinity of different groups, the unity of 

 types of structure, the representative forms through which 

 foetus passes, the metamorphosis of organs, the abortion of 

 others, cease to be metaphorical expressions and become 

 intelligible facts" (p. 50). 



In general, organisms can be understood only if we take 

 into account the cardinal fact that they are historical beings. 

 ' We must look at every complicated mechanism and instinct 

 as the summary of a long history of useful contrivances much 

 like a work of art" (p. 5I). 1 



Already in 1842 Darwin had seized upon the main 

 principles of evolutionary morphology : the indications then 

 given are elaborated in the thirteenth chapter of the Origin 



1 Cf. a parallel passage in the Origin^ 1st ed., pp. 485-6. 



