138 ORIGIN OF YOLK IN OVA OF AN ENDOPARASlTIC COPEPOD, 



chromatin, and the kaiyosomes He free in the nucleoplasm. The 

 period is characterised by the disintegration of the chromatin- 

 reticulum formed during the last period. 



The fine granules of chromatin next begin to increase in size, 

 and lose in depth of staining, until, instead of being opaque 

 black points, they become semi-translucent, purple spherules. The 

 karyosomes meanwhile remain unchanged (Fig. 4). This pheno- 

 menon, I regard as the formation of the first yolk-granules. 

 During succeeding stages, they continue to increase in size. 



The karyosomes very soon exhibit signs of activity. Each of 

 them, from a solid sphere of chromatin, becomes converted into 

 a small, spongiform mass (Fig. 5), probably due to the formation 

 of vacuoles within them. What this activity, which characterises 

 the period, means, I am quite unable to say, but I do not think 

 that it can affect the deductions made later. 



Meanwhile, the nucleus has so increased in size, that it is now 

 surrounded by a mere envelope of cytoplasm, the presence of 

 the nuclear membrane being evidenced more by the definite out- 

 line of the nucleus, than by the actual visibility of the membrane. 



The next period is characterised by the formation of a new 

 and much smaller nucleus within the old. This takes place in 

 three steps. 



Around one, or it may be two. or three, coalescent, spongiform 

 karyosomes, there becomes recognisable an area of plasm devoid 

 of the spherules, which are scattered plentifully throughout the 

 rest of the nucleus, and this area of plasm takes a faint purple 

 stain (Fig. 6). 



This purple-staining globule of plasm, with its contained karyo- 

 some or karyosomes, by this time quite coalesced, is next enclosed 

 in a distinct membrane (Fig. 7). 



The karyosome once more assumes a solid spherical form, the 

 surrounding plasm still staining purple. 



This area henceforward constitutes the nucleus of the cell; it 

 is shown in Fig. 8, which is a section of a mature, primary oocyte. 



Meanwhile the remaining karyosomes, scattered throughout the 

 old nuclear area, have also shrunken to their previous size and 



