REPETITION OF PAST HISTORY. 12$ 



a summary of past history, it is a key to the prob- 

 lem of the origin of the animal kingdom as it exists 

 to-day. 



For the pursuance of this study three tasks are 

 necessary: (i) We must discover whether or not 

 this assumption is true ; (2) we must find, if possi- 

 ble, an explanation of the fact, if its truth is demon- 

 strated ; and (3) we must apply the principle in 

 every conceivable direction, and construct, as far as 

 possible, the history of the animal kingdom, in order 

 to discover if the result be in harmony with the evi- 

 dence from other sources. A perfectly satisfactory 

 answer cannot as yet be given to any of these ques- 

 tions ; but the evidence is daily increasing, and it is 

 not difficult to see what the final result will be. 



I. As to the Truth of the Assumption that Embry- 

 ology Repeats Past History. 



Several methods of investigation are here possible. 

 The simplest, and the one most readily suggesting 

 itself, is to compare the history of animals as taught 

 by embryology with their history as taught by fos- 

 sils. If it could be shown that the two agree per- 

 fectly, we should have a demonstration of the point. 

 But this is obviously at present impossible. Such 

 an exact comparison can only be made when we 

 have complete, both the fossil and embryological 

 history of all animals, and our knowledge of both of 

 these subjects is as yet very imperfect. That there 

 is a general parallelism between the two is every- 

 where acknowledged ; indeed, it was recognized half 

 a century ago to its fullest extent by Louis Agassiz. 



