Embryology. 99 



in the life-history of existing deer. Or, in other 

 words, the antlers of an existing deer furnish in their 

 development a kind of resume, or recapitulation, of the 

 successive phases whereby the primitive horn was grad- 

 ually superseded by horns presenting a greater and 

 greater numberof prongs in successive species of extinct 

 deer (Fig. 26). Now it must be obvious that such a re- 

 capitulation in the life-history of an existing animal of 

 developmental changes successively distinctive of sundry 

 allied, though now extinct species, speaks strongly in 

 favour of evolution. For as it is of the essence of this 

 theory that new forms arise from older forms by way 

 of hereditary descent, we should antecedently expect, 

 if the theory is true, that the phases of development 

 presented by the individual organism would follow, in 

 their main outlines, those phases of development 

 through which their long line of ancestors had passed. 

 The only alternative view is that as species of deer, 

 for instance, were separately created, additional prongs 

 were successively added to their antlers ; and yet 

 that, in order to be so added to successive species, 

 every individual deer belonging to later species was 

 required to repeat in his own lifetime the process of 

 successive additions which had previously taken 

 place in a remote series of extinct species. Now I 

 do not deny that this view is a possible view ; but I 

 do deny that it is a probable one. According to 

 the evolutionary interpretation of such facts, we can 

 see a very good reason why the life-history of the 

 individual is thus a condensed resum^ of the life- 

 history of its ancestral species. But according to the 

 opposite view no reason can be assigned why such 

 should be the case. In a previous chapter — the 



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