ON THE NUMBER OF POLAR BODIES, 



ETC. 



-M- 



CONTENTS. 



I. Parthenogenetic and Sexual Egg 



The process of the formation of polar bodies very widely 



distributed ......... 



The significance of polar bodies according to Minot, Balfour, 



and van Beneden ........ 



My hypothesis of the removal of the histogenetic part of the 



nucleus .......... 



Confirmation by the discovery of polar bodies in partheno- 

 genetic eggs 



Parthenogenetic eggs form only one polar body, while eggs 



requiring fertilization form tivo ..... 

 Parthenogenesis depends upon the fact that the part of the 



nucleus which is expelled from sexual eggs in the 



second polar body remains in the e.gg 

 History of this discovery ...... 



II. Significance of the second Polar Body 



Refutation of Minot's theory 



The second division of the nuclear spindle involves a reduc- 

 tion of the ancestral germ-plasms .... 



The theoretical necessity for such reduction 



Phyletic origin of the germ-plasms in existing species . 



The necessary reduction takes place by a special form of 

 nuclear division . . . . 



The division which causes this reduction has probably been 

 already observed ....... 



Van Beneden's and Carnoy's observations . 



Two different physiological effects of karyokinesis 



Significance of direct nuclear division .... 



Arguments in support of the view that the division of the 

 egg-nucleus which causes reduction must occur at the 

 end of ovogenetic development ..... 



Such nuclear division is to be found in the formation of the 

 second polar body ........ 



History of the origin of this view 



page 

 349 



349 



350 



351 



355 



356 



358 

 359 



363 

 364 



366 



367 

 368 



369 



371 

 371 

 375 



377 



378 



3l9 

 380 



