2 THE EVOLUTION OF MAN. 



in systematic natural history, can only serve to bring the subject of our 

 study better before us and to render it more manageable ; but not to mark 

 real distinctions between different things." — Bernhard Cotta (1866). 



Oue comparative study of the Anatomy and Ontogeny of 

 the Amphioxus and the Ascidian has afforded us aid, the 

 value of which can hardly be over-estimated, towards 

 acquiring a knowledge of human Ontogeny. For in the 

 first place we have in this way filled up, as regards Anatomy, 

 the wide chasm which in all previous systems of the 

 animal kingdom existed between Vertebrates and Inverte- 

 brates ; and in the second place, in the germ-history of the 

 Amphioxus we have recognized primordial phases of de- 

 velopment, which have long disappeared from the Ontogeny 

 of Man, and which have been lost in accordance with the 

 law of abridged heredity. Of special importance among 

 these phases of development is the Archigastrula, the ori- 

 ginal, genuine Gastrula-form which the Amphioxus has 

 retained up to ihe present time, and which re-appears in 

 the same form in low invertebrate animals of the most 

 diverse classes. 



The germ-history of the Amphioxus and the Ascidian 

 has, therefore, so far perfected our direct knowledge of 

 human genealogy, that, notwithstanding the incompleteness 

 of our empiric knowledge, there is no essential gap of any 

 great moment in the pedigree. We may, therefore, at once 

 proceed to our task, and, aided by the ontogenetic and 

 comparative -anatomical materials at our command, may 

 reconstruct the main outlines of human Phylogeny. The 

 immense importance of the direct application of the funda- 

 mental biogenetic law of the causal connection between 

 Ontogeny and Phylogeny now becomes evident. But, before 



