54 THE EVOLUTION OF MAN. 



boid cell. Even then, the egg was first a Gastrsea-egg, then 

 a Worm-egg, then an Acrania-egg, then a Fish-egg, an Am- 

 phibian-egg, a Reptile-egg, and lastly, a Bird-egg. The egg 

 of the Bird, as it now is, is a most complex historical pro- 

 duct, the result of countless processes of heredity, which 

 have occurred in the course of many millions of years. 139 



The fact that this primitive egg-form, as it first appears 

 in the ovary of the most dissimilar animals, is always of 

 one form, an undifferentiated cell, of the simplest amoeboid 

 character, has already been pointed out as an especially 

 important phenomenon. In this earliest young condition, 

 immediately after the individual egg-cell has originated in 

 consequence of a separation of the cells of the maternal 

 ovary, no essential difference is recognizable in the egg-celJs 

 of the most dissimilar animals. (Cf. Fig. 10, vol. i. p. 134.) It 

 is not till later, when the primitive egg-cells, or the primitive 

 eggs (protova), have absorbed different kinds of nutritive 

 yelk, and have surrounded themselves with variously formed 

 coverings, and in other ways differentiated — it is not till 

 they have in this way changed into after-eggs (metova), 

 that those of different classes of animals can usually be 

 distinguished. These peculiarities of the developed after- 

 egg, the mature egg, are naturally to be considered as only 

 secondarily acquired, by adaptation to the different con- 

 ditions of existence both of the egg itself and of the animal 

 which forms the egg. 



The two first and oldest ancestral forms of the human 

 race, which we have now considered, the Moneron and the 

 Amoeba, are, considered from a morphological point of view, 

 simple organisms and individuals of the first order, Plastids. 

 AH subsequent stages in the ancestral chain are, on the 



