No. 5S9] 



THE EVOLUTION OF THE CELL 



21) 



ingenious speculations of Mereschkowsky, 17 who assumes 

 a double origin for living beings from two sorts of proto- 

 plasm, supposed not only to differ fundamentally in kind 

 but also to have had origins historically distinct. The 

 first type of protoplasm he terms mycoplasma which is 

 supposed to have come into existence during what he calls 

 the third epoch 19 of the earth's history, at a time when 

 the crust of the earth had cooled sufficiently for water to 

 be condensed upon it, but when the temperature of the 

 water was near boiling point ; consequently the waters of 

 the globe were free from oxygen, while saturated with all 

 kinds of mineral substances. The second type of proto- 

 plasm was amoeboplasm, the first origin of which is be- 

 lieved to have taken place during a fourth terrestrial 

 epoch when the waters covering the globe were cooled 

 down below 50° C, and contained dissolved oxygen but 

 fewer mineral substances. Corresponding with the differ- 

 ences of the epoch and the conditions under which they 

 arose, Mereschkowsky 's two types of protoplasm are dis- 

 tinguished by sharp differences in their nature and con- 

 stitution. 



Mycoplasm, of which typical examples are seen in bac- 

 teria, in the chromatin-grains of the nucleus and the 

 chromatophores of plant-cells, is distinguished from 

 amoeboplasm, which is simply cytoplasm, by the follow- 

 ing points. (1) Mycoplasm can live without oxygen, and 

 did so in the beginning at its first appearance when the 

 temperature of the hydrosphere was too high for it to 



