68 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



the turning over, which allows the isolated blastomere to 

 develop as a whole. The regulation of the frog's egg, with 

 regard to its becoming whole, may be called facultative, 

 whilst the same regulation of the egg of Echinus is 

 obligatory. It is not without interest to note that the 

 first two blastomeres of the common newt, i.e. of a form 

 which belongs to the other class of Amphibia, after a 

 separation of any kind, always develop as wholes, their 

 faculty of regulation being obligatory, like that of Echinus. 



Whole or partial development may thus be dependent 

 on the power of regulation contained in the intimate polar- 

 bilateral structure of the protoplasm. Where this is so, 

 the regulation and the differences in development are both 

 connected with the chief relations of symmetry. The 

 development becomes a half or a quarter of the normal 

 because there is only one-half or one-quarter of a certain 

 structure present, one -half or one -quarter with regard 

 to the very wholeness of this structure ; the develop- 

 ment is whole, in spite of disturbances, if the intimate 

 structure became whole first. We may describe the 

 " wholeness," " halfness," or " quarterness " of our hypothetic 

 structure in a mathematical way, by using three axes, at 

 right angles to one another, as the base of orientation. To 

 each of these, x, y, and z, a certain specific state with 

 regard to the symmetrical relations corresponds ; thence 

 it follows that, if there are wanting all those parts of the 

 intimate structure which are determined, say, by a negative 

 value of y, by minus y, then there is wanting half of the in- 

 timate structure ; and this halfness of the intimate structure 

 is followed by the halfness of organogenesis, the dependence 

 of the latter on the intimate structure being established. 



