THEIE SIGNIFICANCE IN HEKEDITY. 363 



number of ancestral germ-plasms which were contained in the 

 mother-nucleus. Whether the loops divide on their way to the 

 poles or at the poles themselves, no difference will be brought about 

 in the number of ancestral germ-plasms which they contain, for 

 this number can neither increase nor diminish. . The quantity of 

 the different ancestral germ-plasms can alone be increased in this 

 way. I am here referring to observations made by Carnoy 1 on 

 the cells which form the spermatozoa in various Arthropods. It 

 must be admitted, however, that these divisions cannot be regarded 

 as ' reducing divisions,' if Flemming's 2 suggestion be confirmed, 

 that in all these observations the fact has been overlooked that the 

 equatorial loops are not primary but secondary, and that they have 

 arisen from the longitudinal splitting of the nuclear thread during 

 previous stages of nuclear division. But this point can only be 

 decided by renewed investigation. Although many excellent re- 

 sults have been obtained in the subject of karyokinesis, there is still 

 very much to be learnt before our knowledge is complete ; and this 

 is not to be wondered at when we remember the great difficulties in 

 the way of observation which are chiefly raised by the minute size 

 of the objects to be investigated. Flemming's most recent publica- 

 tions prove that we are still in the midst of investigation, and that 

 highly interesting and important processes have hitherto escaped 

 attention. A secure basis of facts is only very gradually obtained, 

 and there are still many conflicting opinions upon the details of this 

 process. I should therefore consider it to be entirely useless, from my 

 point of view, to enter into a critical examination of everything 

 known about all the details of karyokinesis. I am quite content to 

 have shown how it may be imagined that the reduction required by 

 my theory takes place during nuclear 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 must take place, even if they are not supplied 

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



1 Carnoy, 'La Cytodirfese chez les Arthropodes.' Louvain, Gand, Lierre, 1885. 



2 Flemming, 'Neue Beitrage zur Kenntniss der Zelle.' Arch. f. mikr. Anat. 

 Bd. XXIX, 188',. 



