364 ON THE NUMBER OF POLAR BODIES AND 



kinesis according- to the different physiological effect of the process. 

 First, a karyokinesis by means of which all the ancestral germ-plasms 

 are equally distributed in each of the two daughter -nuclei after 

 having been divided into halves : secondly, a karyokinesis by means 

 of which each daughter-nucleus receives only half the number of 

 ancestral germ-plasms possessed by the mother-nucleus. The former 

 may be called ' equal division,' the latter ' reducing division.' Of 

 course these two processes, which differ so greatly in their effects, 

 must also be characterized by morphological differences, but we 

 cannot assume that the latter are necessarily visible. Just as, during 

 the division of the first and second nuclear spindle in the egg of 

 Ascaris megalocephala, karyokinesis takes, upon the whole, the same 

 morphological course, although we must ascribe different physio- 

 logical meanings to the two processes of division, so it may be in 

 other cases. The ' reducing division ' must be always accompanied 

 by a reduction of the loops to half their original number, or by a 

 transverse division of the loops (if such division ever occurs) ; 

 although reduction can only occur when the loops are not made up 

 of identical pairs. And it will not always be easy to decide whether 

 this is the case. On the other hand, the form of karyokinesis in which 

 a longitudinal splitting of the loops takes place before they separate 

 to form the daughter-nuclei must always, as far as I can see, be 

 considered as an ' equal division.' In the accompanying figures II 

 and III, diagrams are given illustrating these two forms of karyo- 

 kinesis, but I do not mean to imply that it is impossible to imagine 

 any other form in which they may occur. 



In Figure II a nuclear spindle is seen at A> and at its equatorial 

 zone there are twelve primary loops. The transverse cross-lines 

 and other markings on the loops indicate that they are composed 

 of different ancestral germ-plasms. The loops are shaded differently 

 in order to render the diagram clear. At B six of the loops are 

 seen to have moved to either pole, so that the figure is a repre- 

 sentation of the ' reducing division.' Figure III is a diagrammatic 

 representation of ' equal division.' The six loops at the equatorial 

 zone of A are shown by different cross-lining and shading to be 

 composed of different ancestral germ-plasms. The loops split 

 longitudinally in a direction indicated by the longitudinal line 

 upon each of them. In B the halves of the loops are seen to 

 have moved to the opposite poles of the spindle, so that there 



