OF THE CELL THEORY 183 



third the diameter of the egg itself, and consists of 

 a well-marked nuclear membrane enclosing fluid 

 nucleoplasm in which float a number of chromatin 

 globules of varying size and apparently unconnected 

 with one another. At the time of ripening of the 

 egg, shortly before it leaves the ovary, the nuclear 

 membrane becomes crumpled and indistinct ; the 

 whole nucleus shrivels very greatly, its fluid con- 

 tents being diffused through the egg; the majority 

 of the chromatin globules disappear, but a group of 

 very small ones near the centre persist ; these unite 

 together to form a convoluted varicose chromatin 

 thread which soon breaks up into loops ; then a 

 nuclear spindle appears with which the loops soon 

 become connected as in ordinary mitosis. The 

 spindle with the associated loops, which together 

 are of exceedingly small size, move to the surface 

 of the ovum ; the loops and the spindle now divide 

 in the ordinary way into two equal halves which 

 become the daughter nuclei. One of the daughter 

 nuclei is extruded as the first polar body, while the 

 other retreats into the interior of the egg. The 

 formation of the second polar body is a repetition 

 of the process by which the first was formed. As 

 the amount of chromatin is halved at each nuclear 

 division, the female pronucleus, which is the 

 portion of the egg nucleus left after the formation 

 of the second polar body, will contain exactly one- 

 fourth of the amount of chromatin present in the 

 egg nucleus at the formation of the nuclear spindle. 

 Van Beneden's account of the process in Ascaris 

 agrees exactly with this. At each division of the 



