REGENERATION AND DEATH 175 



Hertwig of Munich. As we have learned that the 

 proportion of the nucleus and the protoplasm is so 

 important, we must attribute to this alteration in the 

 dimensions of the nucleus during segmentation great 

 significance. 



We have next a series of figures which have inter- 

 ested me very much and which I only recently secured 

 as the result of studies I have been making in my own 

 laboratory at the Harvard Medical School. These 

 pictures are now shown publicly for the first time, and 

 record a fact which, so far as I know, has never yet 

 been clearly noted and recognised as important by any 

 investigator. The four drawings at the top, Fig. 61, 

 represent four single nuclei taken from different parts 

 of a rabbit seven and one half days after the com- 

 mencement of its development. The second set of 

 drawings, 5, 6, 7, 8, show nuclei from different char- 

 acteristic parts of a rabbit embryo of ten days. Note, 

 please, the size of these nuclei, the curious network of 

 threads in their interior, and the existence, generally 

 more or less in a central position, of a mass of material 

 which stands out conspicuously and represents a con- 

 densation of the nuclear stuff at that particular point. 

 Such a central body is highly characteristic of these 

 early stages. Next we come in the series of draw- 

 ings from 9 to 20, stretching across the screen in two 

 lines, to a rabbit embryo of twelve and one half days. 

 Instead of having nuclei of large size we have now 

 nuclei which are obviously small. Instead of having 

 nuclei which are more or less alike in appearance, we 



