THE MODERN STUDY OF ZOOLOGY 25 



mately by a series of steps, which space forbids me 

 to notice, to the promulgation of what is known as 

 the recapitulation hypothesis. This which is found 

 lurking in the works of von Baer, but first received 

 definite expression from Fritz Muller, is commonly 

 stated thus : The development of the individual is 

 an epitome of the development of the species i.e., the 

 actual changes through which an animal passes in 

 its development from the egg to the adult repre- 

 sent in a condensed form its genealogical history or 

 pedigree. 



Thus embryology provides us with a completely 

 new and very accessible clue to the determination 

 of animal genealogies a clue of such extreme 

 value that we cease to wonder at the immense 

 importance attached to it by the modern zoologist, 

 or at the time and perseverance that are expended 

 in attempts to penetrate its mysteries. For the 

 clue thus afforded is the one on which we have 

 chiefly to rely in our efforts to unravel the knotty 

 problems of genealogy, and it is a clue in the 

 following up of which extreme caution is necessary. 

 If the recapitulation hypothesis were strictly true, 

 if the ontogenetic history of an individual were an 

 accurate and complete reflection of its specific 

 history or phylogeny, then our task would be a 

 comparatively light one. But it is not so. As 

 Fritz Miiller has pointed out with admirable clear- 

 ness* the ontogeny of an individual is not a simple 

 abbreviated history of its phylogeny, but a history 

 obscured and falsified by a variety of causes, the 



* Fur Darwin (English translation), chap. xi. f pp. no seq. 



