Organisms from Eggs 129 



demonstrated the existence of a very simple but definite 

 structure in the unfertilized egg of the sea urchin; and 

 a similar simple structure has been demonstrated by 

 other authors, especially Conklin, in the eggs of other 

 forms. 



In this chapter we shall attempt the task among 

 others of showing how, on the basis of the simple physi- 

 cochemical structure of the unfertilized egg, the main 

 organ of self-preservation of the organism, the intestine, 

 is formed through the mere process of cell division and 

 growth. Cell division is the most general of the specific 

 functions of living matter and it is the basis underlying 

 the differentiation of the comparatively simple struc- 

 ture of the egg into a more complex organism. If cell 

 division and growth were equal in all parts of the egg 

 no differentiation would be possible, but the different 

 regions of the unfertilized egg contain different consti- 

 tuents and these, probably on account of their chemical 

 difference, do not all begin to grow or divide simulta- 

 neously and equally. 



Boveri 1 found that in the unfertilized egg of the sea 

 urchin Strongylocentrotus lividus at Naples a definite 

 structure is indicated by the fact that the yellowish-red 

 pigment is not equally distributed over the whole 

 surface of the egg but is arranged in a wide ring from 

 the equator almost to one of the poles. Thus three 



1 Boveri, Th., Verhandl. d. physik.-med. Gesettsch., Wurzburg, 1901, 

 xxxiv., 145. 

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