DURATION OF HUMAN GERM-HISTORY. 5 



do not reflect that the very same marvel actually recurs 

 before our eyes in the short space of nine months during 

 the embryonic development of each human individual. 

 The same series of multifariously diverse forms, through 

 which our brute ancestors passed in the course of many 

 millions of years, has been traversed by every Man during 

 the first 40 weeks of his individual existence within the 

 maternal body. 



All changes in organic forms, all metamorphoses of 

 animal and plant forms, appear to us all the more remark- 

 able and all the more wonderful in proportion as they occur 

 more rapidly. When, therefore, our opponents pronounce that 

 the past development of the human race from lower animal 

 forms is incredible, they must regard the embryonic develop- 

 ment of the human individual from the simple egg-cell as 

 far more wonderful in comparison. This latter process — the 

 ontogenetic modification — which takes place before our eyes, 

 must appear more wonderful than the phylogenetic modifi- 

 cation, in proportion as the duration of the tribal history 

 exceeds that of the germ-history. For the human embryo 

 must pass through the whole process of individual develop- 

 ment, from the simple cell up to the many-celled perfect 

 Man, with all his organs, in the brief space of 40 weeks. On 

 the other hand, we may assign many millions of years for 

 the accomplishment of the analogous process of phyloge- 

 9 netic development — the development of Man's ancestors from 

 the simplest one-celled form. 



As regards these phylogenetic periods, it is impossible 

 to fix approximately their length in hundreds or in thousands 

 of years, or to establish any absolute measure of their 

 duration. But the researches of geologists have long since 



