296 BULLETIN OF THE 



toward the ends of the nucleus without fully reaching them. As the 

 rods (Stiibchen) of the middle zone arise by a differential process which 

 separates "nuclear substance" from "nuclear sap," so the new nuclei 

 arise by the reverse process, — the rods imbibe nuclear sap, swell, and 

 form granules which melt together to constitute the nuclear mass. A con- 

 densation of nuclear substance is likewise the cause of the dark granule 

 at the end of the spindle and the dark streak at the end of the nuclear 

 band. The " Radienfiguren " consist in a radial grouping of the proto- 

 plasm around the nucleus or definite points of the same. 



It is concluded, further, that " the division of the nucleus is a process 

 entirely independent of the division of the protoplasm," since in certain 

 eggs, which probably had gradually succumbed to the effect of external 

 noxious influences, the division of the nucleus was not followed by a cor- 

 responding process on the part of the protoplasm. 



The two main results which Hertwig deduces from the foregoing are : — ^ 

 (1.) In egg segmentation a dissolution of the nucleus does not take place ; 

 the iluclei of the segmentation spheres are rather parts (Theilstiicke) of 

 the maternal nucleus. The supposed disappearance of the nucleus be- 

 fore division is explainable from its peculiar changes of form, by reason 

 of which it becomes less easily recognizable in the living object. (2.) In 

 cell life a high physiological significance belongs to the nucleus, for it 

 must be considered as an automatic force-centre. In cell multiplication 

 this especially comes into activity, inasmuch as it impels and regulates 

 the same. 



For the most part I can only confirm the views entertained by Hert- 

 wig ; in one or two points, however, I find a difficulty in adopting his 

 opinions. The amoeboid changes of form which the nucleus presents are 

 probably referable to an inherent activity of the nucleus, which warrants 

 the conclusion that it is an automatic centre in the cell ; it seems less 

 certain that the elongation of the nucleus and the appearance of two 

 centres of attraction are referable to the same force resident in the nu- 

 cleus. In the first place, only two substances are recognized as entering 

 into its composition, — a nuclear sap and a nuclear " substance." The 

 latter is the active component. If, as Hertwig seems to infer, that part 



as seem« to be the case, Priestley entertained the opinion that Hertwig had failed 

 to draw and to formally express a conclusion establishing a genetic connection between 

 the new nuclei and the median zone, then it is probable that the following passage 

 must have been overlooked by him : " Aus der Aufeinanderfolge der verschiedenen 

 Bilder glaube ich den Schluss ziehen zu diirfen, dass die beiden seitlichen Verdich- 

 tungszonen aus der mittleren entstanden sind." (Hertwig, p. 414.) 



I 



