144 



THE EVOLUTION OF MAN. 



are quite visible to the naked eye ; but the greater number 

 are microscopic. Our reasons for regarding the Amoebae as 

 the particular one-celled organisms, the phylogenetic rela- 

 tions of which to the egg-cell are of peculiar importance, 

 will be evident from the following facts. In many lower 

 animals, the egg-cell remains in its original, naked condition 

 till it is fertilized ; it acquires no covering, and is often 

 indistinguishable from an Amoeba. Like the latter, these 

 naked egg- cells can extend processes and move about. In 

 the Sponges, these active egg-cells creep freely about, as 

 though they were independent Amoebae (Fig. 14), even 



Fig. 14.— Egg-cell of a Chalk Sponge (Olyn- 

 thus). The egg-cell moves and creeps about within 

 the Sponge, by means of variable processes which 

 it extends. It is not distinguishable from the 

 common Amoeba. 



within the parent organism. In this 

 condition they were observed by earlier 

 naturalists, and were mistaken for 

 Amoebae, living as parasitical intruders in the body of 

 the Sponge. It was only afterwards that it was dis- 

 covered that these supposed one-celled parasites were in 

 reality the egg-cells of the Sponge itself. This remarkable 

 phenomenon is also found in other lower animals, for ex- 

 ample, in those pretty bell-shaped Plant-animals (Medusce) ; 

 the eggs of these also remain as naked, uncovered 

 cells, which stretch out amoeboid processes, feed themselves, 

 move, and from which, after fertilization, the many-celled ' 

 Medusa-organism is indirectly or directly developed by 

 repeated division. 



It is, therefore, certainly no wild hypothesis, but an 



