DEVELOPMENT OF DISTICHOPORA VIOLACEA. 131 



periphery for a very considerable time, for of the numerous 

 unfertilised ova that I have examined a large majority have 

 their germinal vesicles in that position. 



In the next stage the membrana limitans of the inner half 

 of the vesicle disappears, the network and the germinal spot 

 break down into numerous very minute scattered granules 

 (%. 7). 



Then the membrana limitans entirely disappears, and lastly, 

 the substance of the vesicle, or, as it should now be called, the 

 oosperm nucleus, becomes scattered through the substance 

 of the ovum. 



Fig. 8 is a careful drawing of a stage in which the mem- 

 brana limitans has just disappeared, and I have three or four 

 complete series of sections through ova in which no trace of 

 nuclear structure can be found nor any area, such as that 

 shown in this figure, which represents the vanished nucleus. 



As these two stages are of the greatest importance in the 

 consideration of what follows, it is necessary to say that not- 

 withstanding very careful search with high powers, no trace 

 of karyokinetic figures could be observed. 



The ova of these stages are not sufiiciently numerous, nor 

 are the methods of preservation sufficiently perfect to enable 

 one to assert that such figures do not occur. Corrosive sub- 

 limate followed by alcohol, although giving excellent general 

 histological results, does not always bring out the full details 

 of nuclear division ; and it will be necessary to confirm these 

 purely negative results as regards karyokinesis by observa- 

 tions made upon specimens preserved in Flemming's solution 

 and other reagents before any general statements regarding 

 fragmentation of the oosperm nucleus of Distichopora can be 

 accepted. 



Nevertheless it is my belief that we have here an instance 

 of nuclear fragmentation, for reasons which I propose to dis- 

 cuss in the third section of this paper. 



In the next stage that I have observed, a few small islands of 

 protoplasm may be seen in the yolk (fig. 9), and the exa- 

 mination of broken sections, in which part of the yolk has 



