THE RECAPITULATION HYPOTHESIS. 309 



degree remarkable that all vertebrate animals of the most 

 different classes — fishes, amphibious animals, reptiles, birds, 

 and mammals — in the first periods of their embryonic 

 development cannot be distinguished at all, and even much 

 later, at a time when reptiles and birds are already distinctly 

 different from mammals, that the dog and the man are 

 almost identical ? Verily, if we compare those two series of 

 development with one another, and ask ourselves which of 

 the two is the more wonderful, it must be confessed that 

 ontogeny J or the short and quick history of development of 

 the individual, is much more mysterious than i~>hylogeny, or 

 the long and slow history of development of the tribe. For 

 one and the same grand change of form is accomplished by 

 the latter in the course of many thousands of years, and by 

 the former in the course of a few months. Evidently this 

 most rapid and astonishing transformation of the individual 

 in ontogenesis, which we can actually point out at any 

 moment by direct observation, is in itself much more 

 wonderful and astonishing than the corresponding, but 

 much slower and gradual transformation which the long 

 chain of ancestors of the same individual has gone through 

 in phylogenesis. 



The two series of organic development, the ontogenesis of 

 the individual and the phylogenesis of the tribe to which 

 it belongs, stand in the closest causal connection with each 

 other. I have endeavoured, in the second volume of the 

 " General Morphology," * to establish this theory in detail, 

 as I consider it exceedingly important. As I have there 

 shown, ontogenesis, or the develoj^TYient of the individual, is a 

 short and quick repetition (recapitulation) of phylogenesis, 

 or the development of the tribe to ivhich it belongs, determined 



