52 THE EVOLUTION OF MAN. 



We have already explained the one-celled germ-form 

 which we see in the original egg-cell and the parent-cell 

 which is originated by the fertilization of the egg-cell, as 

 the reproduction of a one-celled parent-form, to which we 

 ascribed the organization of an Amoeba (cf. Chap. VI.). For 

 the Amoeba, as it yet lives widely distributed in the fresh 

 and salt waters of the globe, must be regarded as the most 

 unditierentiated and most original of the various one-celled 

 Primitive Animals. As the immature primitive egg-cells 

 (which as "primitive eggs" or Protova are found in the 

 ovary of animals) are indistinguishable from ordinary 

 Amoebae, we are justified in pointing to the Amoeba as the 

 one-celled phylogenetic form, which, in accordance with the 

 fundamental law of Biogeny, is at the present time yet 

 reproduced in the ontogenetic primitive condition of the 

 " Amoeboid egg-cell." As evidence of the striking cor- 

 respondence of the two cells, it was incidentally men- 

 tioned that in the case of some Sponges the real eggs of 

 these animals were formerly described as parasitic Amoebae. 

 Large one-celled Amoeba-like organisms were seen creeping 

 about in the interior of the Sponge, and were mistaken for 

 parasites. It was only afterwards that it was discovered 

 that these "parasitic Amoebae" (Fig. 168) are really the eggs 

 of the Sponge, from which the young Sponges develop. 

 These egg-cells of the Sponge are, however, so like the 

 true common Amoebae (Fig. 167) in size and structure, in 

 the nature of their nuclei and in the characteristic form of 

 movement of their continually changing false-feet (pseudo- 

 podia), that, unless their source is known, it is impossible 

 to distinguish them. 



This phylogenetic explanation of the egg-cell and its 



