8o Hypothesis of Structure of Germ Substance 



writes Strassburger, "it is absolutely impossible to hunt 

 out anything but equal division. Unequal division is not 

 presented at all. There is not a single fact to support the 

 notion that it exists." 50 



We shall here limit ourselves to mentioning only two 

 orders of facts which speak directly against unequal divi- 

 sion : 



First, it does not occur in any nucleus in the vast realm 

 of unicellular and of primitive pluricellular forms, con- 

 sisting of colonies of like cells; for in them the facts of 

 heredity show directly that nuclear division is always 

 equal. 



But especially the oft repeated and keenly discussed 

 experiments upon the relative shifting and isolation of 

 blastomeres afford direct proof that nuclear division is 

 equal in the first segmentations of the egg. We recall for 

 example the experiments of Chabry upon the Ascidians, 

 those of Wilson upon Amphioxus, those of Herbst on the 

 separation of the blastomeres of the sea urchin merely by 

 adding chloride of potassium to ordinary sea water, of 

 Driesch on the Echinus microtuberculatus, of Oscar Hert- 

 wig upon frogs' eggs, of Raffaello Zoja on the Medusae 

 and so on. These experiments in which one of the first 

 blastomeres, or one of the four, or eight, or sixteen, or 

 thirty-two first blastomeres, produce when isolated an 

 entire embryo, perfectly formed but proportionally 

 smaller, or in which the blastomeres, though shuffled 

 about in any way whatever, nevertheless developed in a 

 perfectly normal way, lead with the greatest certainty 

 that any one could desire to the conviction that in the 



50 Straburger : Uber periodische Reduktion der Chromosomen- 

 zahl im Entwicklungsgang der Organismen. Biol. Centralbl., XIV. 

 No. 23-24. Leipzig, Dec. i, and 15, 1894. P. 835. 



