358 THE CELL 



means of the process of nuclear division, so that different parts of 

 the cells acquire the different properties, which are subsequently 

 developed in them. According to this view, the essential nature 

 of development would consist in gradually separating all the 

 elemental germs, taken collectively, which the idioplasm or the 

 fertilised egg contains, into constituent parts, and of distributing 

 them differently, both as regards time and place, Only those cells, 

 which function in the reproduction of the organism, are supposed 

 to be exceptions to this rule, and to receive again the whole collec- 

 tion of the elemental germs during the processes of development. 

 Hence a twofold mode of distributing the idioplasm is assumed to 

 occur, one by the growth and halving of similar germs, and one by 

 the resolution into different component parts of dissimilar ones. 



It is difficult to imagine how such a process can actually take 

 place in any concrete case. Further, this assumption does not 

 agree with the above-mentioned facts of reproduction and regener- 



1 ation ; for instance, in plants and in the lower animals, almost any 

 collection of cells is able to reproduce the whole ; and again, cells 

 may alter their functions, as seen in the phenomena of regeneration. 

 Therefore, the views which I have frequently upheld (IX. 10-13), 

 and which agree with those held by Nageli and de Vries, etc., 

 seem to be more probably true, that as a rule each cell of an 

 organism receives all the different kinds of elemental germs from 



' the egg-cell, and that its especial nature is solelv determined by its 

 conditions, only certain individual elemental germs or idioblasts 

 becoming active, whilst the others remain latent. 



But in what manner can individual idioblasts become active, 

 and thus determine the nature of the cell ? Two hypotheses have 

 been suggested in answer to this question, a dynamic one by 

 Nageli (IX. 20), and a material one by de Vries (IX. 30). In 

 order to explain the specific activity of idioplasm, Nageli assumes 

 that " occasionally a definite colony of micellae, or a combination 

 of such colonies, become active," that is, " are thrown into definite 

 conditions of tension or motion," and he considers that "this local 

 irritation, by means of dynamic influence, and the transmission of 

 peculiar conditions of oscillation acting at a microscopical distance, 

 governs the chemical and plastic processes." " It produces fluid 

 trophoplasm in enormous quantities, and by its help effects the 

 formation of non-albuminous constructive material, of gelatinous, 

 elastic, chitinous, cellulose-like substances, etc., and it gives to this 

 material the desired plastic form. Which micella group of the 



