OF THE CELL THEORY 179 



versal : a point on which Waldeyer differs from 

 him emphatically. 



On the whole it would appear that the balance 

 of evidence is against the existence of a sharp 

 distinction between the direct and indirect methods 

 of nuclear division ; and in favour of there being 

 one common form, subject to considerable variation 

 in detail. Much however yet remains to be done 

 before the question can be regarded as settled. 

 We are at present absolutely in the dark as to the 

 real meaning and significance of the chromatin 

 threads ; and it is especially important that the true 

 relation of van Beneden's pole-bodies and of the 

 nuclear spindle should be clearly determined, for 

 until this is done, no theory of nuclear division can 

 be held to be definitely established. Perhaps the 

 most striking points brought to light by the recent 

 researches on nuclear division are the extreme 

 complication of a process formerly regarded as a 

 perfectly simple one, and the mathematical precision 

 with which the division of the chromatin into equal 

 halves is effected in typical cases. 



One of the most interesting problems arising 

 from the advance of our knowledge concerning the 

 minute changes that occur during nuclear division, 

 is the relation of the phenomena of mitosis to the 

 act of fertilisation of the egg. By the older writers 

 it was supposed that either prior to, or as a con- 

 sequence of the act of fertilisation, the nucleus of 

 the egg, or germinal vesicle as it is commonly 

 termed, disappears completely. It is now however 

 known that part of the egg-nucleus persists and 



