1 6 THE STRUCTURE OF CELLS 



a well-defined nuclear body, by a division of the nucleus. This 

 may either take place in a simple manner, as was determined by 

 Eemak, or it may only be secured as the result of a complicated 

 rearrangement and fission of certain nuclear constituents. To the 

 former, or direct (Flemming), method of division, the termAmitosis has 

 been applied by Flemming, whilst the latter, or indirect (Flemming), 

 method was also termed Mitosis by the same author. The word 

 Karyokinesis (Schleicher) has often been substituted for mitosis, but 

 both terms are expressive of the same phenomena. Amitosis, in 

 the higher animals, is not of such generally widespread occurrence, 

 but in the lower forms it frequently appears as an intercalated 

 method along with a more or less complex form of ordinary 

 karyokinesis. It is also generally met with in nutritive gland cells; 

 thus in the follicular epithelium of the ovary, in the "foot " cells of the 

 testis, and in the tapetal cells of the higher plants, it is not uncom- 

 mon. In these cases it appears to be characteristic of degenerating 

 tissues, and this explanation has been extended to amitosis gener- 

 ally by Ziegler and vom Rath, but many instances are known in 

 which such a view is quite untenable. Thus, there is good reason 

 to believe, as Meves or others have shown, that in the ovary, cells 

 which ultimately are destined to give rise to ova may multiply in 

 this way, and Schaudinn, Siedlecki, and others have shown that in the 

 Sporozoa such amitotic divisions often follow shortly on the act of 

 fertilisation, and give rise directly to the new generation of parasites, 

 and again amongst Infusoria the macronucleus seems always to in- 

 crease in this way. Furthermore, Nathansohn proved, in the case 

 of Spirogyra, that by appropriate treatment with anaesthetics the 

 nuclei could be induced to divide amitotically, and that this amitotic 

 origin in no way influenced the conditions of the subsequent develop- 

 ment of the cells concerned, for these were capable of even pro- 

 ceeding as far as to form sexual cells, on the restoration of a normal 

 environment. But in comparing amitosis and mitosis together, the 

 advantage which the latter possesses, so far as can at present be 

 stated, seems to lie in the accurate quantivalent distribution of all 

 the structural elements concerned in the process between the two 

 daughter nuclei. Whether this is the only advantage, or whether 

 perhaps some mechanical or other factors are also involved, must be 

 left to the future to decide. 



In considering the general phenomena presented by karyokinesis, 

 there are two sets of factors which, though closely interwoven in 

 the process, may with advantage be kept as distinct as possible. 

 For these changes involve the nucleus on the one hand and the 

 cytoplasm on the other, and the degree of complexity which each 

 of them may respectively assume is not necessarily invariable or 

 correlative, either in different organisms or in different tissues of 

 the same individual. A second, and not less important, considera- 



