190 SOME RECENT DEVELOPMENTS 



the processes of sexual reproduction, but occur as 

 characteristically in the act of division of an ordinary 

 epithelial cell as in the formation of a polar body 

 by a ripe ovum. 



It is well also to bear in mind that although 

 the arrangements and divisions of the chromatin 

 threads naturally attract special attention, it is by 

 no means certain that these threads are the main 

 factors in the act of nuclear division. Indeed the 

 comparison of the direct method of division with 

 the indirect method which we have discussed 

 above, rather suggests that the nucleoplasm or 

 nuclear substance itself is the really essential 

 element, and that the chromatin threads need not 

 even be present, at any rate in a form capable of 

 being brought into view by the reagents at present 

 in use. 



And so it would appear from these more recent 

 researches, of which time has only permitted me to 

 give a brief and most imperfect summary, that the 

 cell theory, great and important as it is most 

 undoubtedly, is rather the commencement of a 

 great movement, a fresh starting-point from which 

 to begin investigations anew, than a complete 

 scheme or final explanation ; and the one great 

 lesson for us to learn is that processes of 

 apparently the simplest kind are really of an 

 extremely complicated nature, and will well repay 

 the most minute and attentive study : for a right 

 understanding of the changes that occur during the 

 act of division of an ordinary epithelial cell, and 

 of the causes determining those changes, would 



