IMULTIPLICATIOX OF CELLS. 13 



at one time dispersed through the whole cell and its branches, but at another 

 time they gather into a heap in the central part, leaving the rest of the branched 

 cell vacant, but \s'ithout alteration of its figui-e. In the foiTaer case the skin is 

 of a dusky hue ; in the latter, pale. Like the movements of the protoplasm, the 

 aggi-egation of the pigment molecules can be excited thi'ough the nerves, both 

 mechanicallj' and electrically. 



The fact above mentioned, that these movements of cells may be excited by 

 stimulation of the nerves, is especially worthy of note, in as much as it proves 

 that operations effected in and by cells are more or less under the governance of 

 the neiTOUs system. Moreover, the well known influence of mental states over 

 the secretions, and the effects resulting from experimental stimvilation of the 

 nei-ves of secreting glands, although doubtless due in pait to changes in the 

 blood-vessels, seem to show that this subjection to the nervous system extends 

 even to the chemical and physical operations which take place in secreting cells. 

 A ciuious and interesting observation in proof of this is adduced by KoUiker. 

 He found that the light of the fii-efly, lamj>//ris. is emitted from cells in which 

 albuminoid matter is decomposed with production of ui-ate of ammonia, and that 

 the emission of light could be brought on or rendered more vivid by electrical 

 and other stimuli operating through the nerves. 



The well-known tremulous movement which so often affects minute particles 

 of matter, is not unfrequently observed in the molecular contents of cells ; but 

 this phenomenon depends simply upon physical conditions, and is of a totally 

 different character from the motions of the protoplasm above refeiTed to. 



multiplication oi Cells by Division. — The amoeboid movements 

 of the protoplasm are directly concerned in the process of subdivision 

 of a cell. This is more particularly to be observed in the division of a 

 ft'ee cell — a white l)lood-corpuscle, for example — in which the process, 

 as described by Klein and others, is, briefly, as follows (fig. 7) : — One 



Fig. 7. 





Fig. 7.— Stages in the Division of a Coloukless Corpuscle of Newt's Blood 



(after Klein). 



of the processes of an amoeboid corpuscle, the nuc.eus of which has 

 previously undergone division, remains unretracted, and into this one 

 of the nuclei from the Ijody of the cell may pass. The protruded part 

 then becomes more and more withdrawn from the rest of the cell, 

 and, finally, by the rujjtnre of the connecting neck of protoplasm, 

 may become entirely detached, breaking away as an independent 

 corpuscle. 



But the process is commonly of a more simple character, as is the 

 case, for instance, with the process of cleavage, already mentioned 

 in treating of the production of embryonic cells. The actual process 

 of division has now been observed in the ova of many of the lower 

 animals. It is preceded by slow heaving movements of the proto- 

 plasm ; a furrow then apjiears upon the surface, soon to disappear 



