I40 THE EVOLUTION OF MAN. 



of food-yelk is collected within the original yelk, as pro- 

 vision for the growing embryo : various coverings are 

 formed around the egg. The egg-cells of many °>ther 

 animals receive similar internal and external additions. 

 But as these are always of subordinate importance in the 

 formation of the embryo itself, serving either as food, or as 

 a protecting covering for the embryo, we may disregard 

 them entirely, and turn our attention to the most important 

 point, — the essential similarity of the original egg-cells of 

 Man and other animals (Fig 10). 



Let us here make use for the first time of our funda- 

 mental biogenetic law, and a,pply this causal law of develop- 

 ment directly to the human egg-cell. This results in an 

 extremely simple, but highly important conclusion. From 

 the one-celled organization of the human egg and of the 

 eggs of the other animals, the conclusion directly follows, 

 according to this fundamental law of Biogeny, that all 

 animals, including Man, descend originally from a one- 

 celled organism. If that fundamental principle is really 

 true, if germ-history or the development of the individual 

 is an epitome or a brief reproduction of the tribal history or 

 the development of the race (and it is impossible to doubt 

 this), then, from the fact that all eggs are originally simple 

 cells, we must necessarily conclude, that all many-celled 

 organisms are descended from a one-celled organism. As, 

 however, the original egg-cell has the same structure in the 

 case of Man as in that of all other animals, we may reason- 

 ably assume that this one-celled original form was probably 

 the common one-celled ancestral organism of the whole 

 animal kingdom, including Man. But this last hypothesis is 

 by no means as certain as the former conclusion. 



