AJMGEBOID ANCESTORS. 29 



Our task of ascertaining a pedigree of Man thus widens 

 into the more considerable task of constructing the pedigree 

 of all the Vertebrates. This is connected, as we learned from 

 the Comparative Anatomy and Ontogeny of the Amphioxus 

 and of the Ascidian, with the pedigree of the Invertebrate 

 animals, and directly with that of the Worms, while no con- 

 nection can be shown with the genealogy of the indepen- 

 dent tribes of the Articulated Animals (Arthrojjoda), Soft- 

 bodied Animals (MoUusca), and Star-animals {Echinoderma). 

 As the Ascidian belongs to the Mantled Animals {Tunicata), 

 and as this class can only be referred to the great Worm 

 tribe, we must, aided by Comparative Anatomy and Onto- 

 geny, further trace our pedigree down through various stages 

 to the lowest forms of Worms. This necessarily brings us 

 to the Gastrfiea, that most important animal form in which 

 we recognize the simplest conceivable prototype of an animal 

 with two germ-layers. The Gastrsea itself must have ori- 

 ginated from among those lowest of all simple animal forms, 

 which are now included by the name of Primitive Animals 

 (Protozoa). Among these we have already considered that 

 primitive form which possesses most interest for us — the 

 one-celled Amoeba, the peculiar significance of which depends 

 on its resemblance to the human egg-cell. Here we have 

 reached the lowest of those impregnable points, at which 

 the value of our fundamental law of Biogeny is directl}? 

 found, and at which, from the embryonic evolutionary stage, 

 we can directly infer the extinct parent-form. The amoeboid 

 nature of the young egg-cell, and the one-celled condition 

 in which each Man begins his existence as a simple parent- 

 cell or cytula-cell, justify us in afllrming that the oldest 

 ancestors of the human race (as of the whole anirnal 

 kingdom) were simple amoeboid cells. 



