328 l\i:i'()kr S.A.A. Advaxcemem' of Science. 



lowest organisms, indicates that the division of the cell substance 

 into chromatin and cytoplasm is of fundamental importance. Ac- 

 cording to our view the meaning of this division is to be found in 

 the necessity for a differentiation of the cell into two ])arts, one 

 external (the cell-body), which responds freely to external stimuli 

 (when suitably placed), and one internally (the nucleus), which is 

 but slowly, and probably through the intermediation of the cell- 

 body, affected by external stimuli, but which, when once so affected, 

 stores up these stimuli for a longer or shorter period, and is capable 

 of giving them out again after the original external stimulus has 

 ceased to operate. 



Just as there must be an equilibration between the entire 

 organism and its environment, so there must also be some kind of 

 equilibration between the cell-body and its nucleus. The cell-body 

 is then acted upon by two sets of forces, the external forces of its 

 environment on the one hand and the internal forces of the nucleus 

 on the other. The forces which we imagine to be stored up within 

 the nucleus to a certain extent control the behaviour of the cell-body 

 and prevent it from altogether changing its characters with every 

 change of environment. Thus we have in the nucleus a complex 

 apparatus by means of which we may [lerhaps explain the production 

 of " after-effects.' 



In the course of ordinary cell-division the elaborate processes 

 of karyokinesis may be supposed to secure the divisi(jn of the nuclear 

 material intO' two halves of equal dynamic value, about each of which 

 the cytoplasm will arrange itself in the same way l>ecause each 

 requires the same form of cell-body to equiUbrate it. 



We find a simple illustration of the equilibration I)etween the 

 cell and its nucleus in the case of the well-known springing monad — 

 Hcteromita. This organism consists of a pear-shaped mass of proto- 

 plasm enclosing a nucleus and provided with two whip-like extensions 

 of the protoplasm, or flagella, whose contractions enable it to move 

 about in the water. One of these flagella jirojects forwarfls from 

 the pointed end of the body, the other is attached to the lower 

 surface. In common with other unicellular organisms Hclcromita 

 sometimes reproduces bv simple cell-division or fission, and this 

 fission may take place either transversely — across the body — or 

 longitudinally — in the length of the body. It is as usual accompanied 

 bv division of the nucleus. When fission takes place transversely 

 it is obvious that the body of the cell must be divided into totally 

 dissimilar halves, one with an anterior flagellum and one without. 

 'J'he ventral flagellum simply splits into two, one of which remains 

 attached to each of the daughter-cells, but no possil)Ie division of 

 the anterior flagellum <-()uld provide l>oth of the new cells with such 

 a structure. What actually happens is that one of the daughter- 

 cells keeps the old anterior flagellum while the other developes an 

 entirelv new one from what was the posterior extremity of the 

 parent. 



These jjhenomena may readilv be explained on the principle of 

 equilibration between the cell and its nucleus, and. so far as I can 



