40 FUNDAMENTAL PROPERTIES 



for the simple amiototic division, as well as for the vastly more 

 complicated process of karyokinesis to which no fui-ther reference 

 will be made at present. 



Although we know that fission need not depend upon the 

 presence and influence of a nucleus, it does not necessarily follow 

 that when such a body has been evolved, it may not be in the 

 unit that possesses it in some way causative of such a phenomenon 

 as fission. Too much doubt and uncertainty exists at present as 

 to the real functions of the nucleus to enable us to come to a 

 well-founded opinion on such a point. The fact that division of 

 the nucleus precedes division of the cytoplasm is by no means 

 conclusive, since there is good reason for believing that its mole- 

 cular composition is more complex and unstable than that of the 

 cytoplasm, and this might be the reason why, when the sum total 

 of molecular changes in the cell are about to eventuate in the 

 formation of two separate centres, such processes should take 

 effect sooner, and proceed more rapidly, in the nucleus than in the 

 body of the cell itself. 



The nucleus is a developmental product resulting from differen- 

 tiation of the cell contents, and it is only natural to suppose from 

 its comparative universality and from the complicated processes 

 taking place in connection with it, when what is known as 

 karyokinesis occurs, that it must be associated with important 

 functions. The results of numerous experimental researches 

 carried on with unicellular organisms of various kinds by Balbiani, 

 Verworn and others, in which sections of such organisms have 

 been made have led to important conclusions. ' Merotomy ' is 

 the term applied to these researches, and they have invariably 

 shown that segments which do not contain a nucleus do not 

 survive ; while those that contain the nucleus live and speedily 

 regenerate their primitive form. This has been shown to hold good 

 for vegetal cells, for naked Rhizopods, as well as for Foraminifera 

 and for Ciliated Infusoria,' so the conclusion seems inevitable that 

 where we have to do with nucleated cells the process of ' assimila- 

 tion ' is only carried on in those segments that chance to contain 

 a nucleus. Growth seems impossible where the nucleus is absent 

 — though only where it is altogether absent, as the remarkable 

 experiments of Balbiani with specimens of Stentor have shown. 



' Balbiani discovered one remarkable exception among these latter organisms 

 since the nucleated merozoites of Paramecia, though they lived for a month or 

 more, showed no evidence of regeneration. 



