VI.] THEIR SIGNIFICANCE IN HEREDITY. 375 



division ; and at the same time to have pointed out that there 

 are already observations which may be interpreted in this 

 sense. But even if I am mistaken in this interpretation, the 

 theoretical necessity for a reduction in the number of ancestral 

 germ-plasms, a reduction repeated in every generation, seems 

 to me to be so securely founded that the processes by which it 

 is effected iruist take place, even if they are not supplied by the 

 facts already ascertained. There must be two kinds of karyo- 

 kinesis according to the different physiological effect of the 

 process. First, a karyokinesis by means of which all the an- 

 cestral germ-plasms are equally distributed in each of the two 

 daughter-nuclei after having been divided into halves : secondly, 

 a kar^^okinesis by means of which each daughter-nucleus re- 

 ceives 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 

 oiAscaris megalocephala, karyokinesis takes, upon the whole, the 

 same morphological course, although we must ascribe different 

 physiological 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 Xh^y 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 karyokinesis, 

 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 equa- 

 torial 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 



