EVOLUTION TRACED BIOCHEMICALLY 45 



bodies of water concentrated the amino acids in them 

 and rendered the synthesis of them to complexes, millions in 

 number, one of which, of special constitution, had, to use 

 Tyndall's expression, "the promise and potency of all 

 terrestrial hfe." 



The animal cell, so far as experimental results indicate, 

 lacks the power of synthesizing any of the amino acids 

 except the simplest, amino acetic, and consequently it 

 must depend on those formed by vegetable cells. It must 

 then have evolved later from cells which had the power of 

 synthesizing their own amino acids, but which tended to 

 vary and to develop ultimately a dependence for these 

 on the hydrolysis of the proteins of vegetable organisms they 

 invaginated. The Protozoa of today, with the exception of a 

 number of forms, derive their amino acids from the hydrolysis 

 of the organisms, animal and vegetable, which they ingest. 



This variation could only have begun after the cell 

 nucleus had fully developed, for mitosis in typical animal 

 cells is so similar in its character to mitosis in typical vege- 

 table cells as to make it difficult to suppose that it originated 

 independently in both kingdoms. The variation could not 

 have developed except after a long time, perhaps millions 

 of years. There would appear to be today descendants of a 

 very early stage in this variation, for Euglena, Peridinium, 

 Ceratium and other flagellates, which at times contain 

 chlorophyl and then synthesize from inorganic elements 

 their own proteins and carbohydrates, and are consequently 

 regarded by some as vegetable organisms, are also by 

 zoologists generally classed as animal forms. It is also 

 remarkable that in these forms the mitotic figure in all its 

 stages is so different from what it is in typical animal and 

 vegetable cells, and so rudimentary in character as to suggest 

 that in these forms are still repeated the nuclear form and 

 structure that obtained in an early stage of the evolution of 

 typical mitosis. 



The fact that the flagellates mentioned could alter 

 with the conditions of their environment their metabolic 

 activities, so as either to be photosynthetic or to depend for 

 their nourishment wholly on ingested food material, is an 

 indication that the primal ancestors of the animal cell 



