258 THE INDUCTIONS OF BIOLOGY. 



two new nuclei; and, by something like a reversal of the 

 stages above described, the chromatin becomes dispersed 

 throughout the substance of each new nucleus. While this 

 is going on the cell itself, undergoing constriction round its 

 equator, divides into two. 



Many parts of this complex process are still imperfectly 

 understood, and various opinions concerning them are cur- 

 rent. But the essential facts are that this peculiar sub- 

 stance, the chromatin, at other times existing dispersed, is, 

 when division is approaching, gathered together and dealt 

 with in such manner as apparently to insure equal quantities 

 being bequeathed by the mother-cell to the two daughter- 

 cells. 



§ 74:d. What is the physiological interpretation of these 

 structures and changes? What function does the nucleus 

 discharge; and, more especially, what is the function dis- 

 charged by the chromatin? There have been to these ques- 

 tions sundry speculative answers. 



The theory espoused by some, that the nucleus is the 

 regulative organ of the cell, is met by difficulties. One of 

 them is that, as pointed out in the chapter on " Structure," 

 the nucleus, though morphologically central, is not central 

 geometrically considered ; and that its position, often near to 

 some parts of the periphery and remote from others, almost 

 of itself negatives the conclusion that its function is directive 

 in the ordinary sense of the word. It could not well control 

 the cytoplasm in the same ways in all directions and at 

 different distances. A further difficulty is that the cyto- 

 plasm when deprived of its nucleus can perform for some 

 time various of its actions, though it eventually dies without 

 reproducing itself. 



For the hypothesis that the nucleus is a vehicle for trans- 

 mitting hereditary characters, the evidence seems strong. 

 When it was shown that the head of a spermatozoon is 

 simply a detached nucleus, and that its fusion with the 



