86 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



for the formation of typical organs only, without any 

 regulability. 



Let us first consider the last case, of which the egg of 

 mollusca is a good type : here there is no equal distribution 

 of potencies whatever, the cleavage-cells of this germ are 

 a sort of real " mosaic " with regard to their morphogenetic 

 potentialities. Is this difference between the germ of the 

 echinoderms and the molluscs to remain where it is, and 

 not to be elucidated any further ? Then there would be 

 rather important differences among the germs of different 

 animals, at least with regard to the degree of the specifica- 

 tion of their cleavage cells, or if we ascribe differences 

 among the blastomeres to the organisation of the fertilised 

 egg ready for cleavage, there would be differences in the 

 morphogenetic organisation of the egg-protoplasm : some 

 eggs would be more typically specialised at the very 

 beginning of morphogenesis than others. 



In the first years of the study of " Entwickelungs- 

 mechanik " I pointed out that it must never be forgotten 

 that the egg itself is the result of organogenesis. If, therefore, 

 there are real mosaic-like specifications in some eggs at 

 the beginning of cleavage, or during it, there may perhaps 

 have been an earlier stage in the individual history of the 

 egg which did not show such specifications of the morpho- 

 genetic structure. Two American authors share the merit 

 of having proved this hypothesis. Conklin showed, several 

 years ago, that certain intracellular migrations and re- 

 arrangements of material do happen in the first stages of 

 ovogenesis in certain cases, but it is to E. B. Wilson 1 that 

 science owes a proper and definitive elucidation of the 



1 Journ. Exp. Zool. 1, 1904. 



