DEVELOPMENT OF PAEAVORTEX GEMELLIPARA 473 

 IV. DEVELOPMENT 



1. Growth of the eggs and consideration of the yolk-7iucleus {mito- 

 chondrial mass) 



Throughout the entire length of the ovary (text jfig. 2) from 

 the point where the oogonia are transformed into oocytes there 

 is a gradual increase in the size of the latter. The nucelus 

 measures at the beginning 0.01 mm.; at the time it leaves the 

 ovary its diameter is about 0.025 mm. During all this growth 

 period the nucleus is in a resting condition, showing a fine chroma- 

 tin reticulum and prominent nucleolus. The latter is at first 

 apparently a sphere whose periphery retains more stain than 

 the center. Often one side of the nucleolus is much darker 

 than the other, so that the pale interior is eccentric. When 

 the cell has passed half the length of the ovary a dark spherule 

 with a light interior appears in the center of the nucleolus (figs. 

 7, 8), and remains until the cell leaves the ovary. 



The term 'resting nucleus' is to be used here only in so far 

 as it apphes to the nucleus as a whole; i.e., it retains its spherical 

 or oval form and its limiting membrane. There is observable, 

 however, a certain activity of the chromatin. While the newly 

 formed oocyte nucleus contains a heavy chromatin reticulum 

 whose strands are quite uniform in thickness, the latter soon 

 became markedly thinner. This is due to the accumulation 

 of a part of the chromatin in one to four masses usually near 

 the nuclear membrane (text fig. 3). These are at first irregular, 

 but soon become rounded so as to resemble the nuleolus in form. 

 Rarely do they attain the size of the latter, however, and never 

 contain a lighter interior ; an intense blue-black iron-haematoxy- 

 lin stain is characteristic of these fragments. 



It is first at this stage that one often finds one or more black 

 bodies of perfectly spherical outline lying in the cytoplasm 

 outside the nucleus. Their appearance is such as to suggest 

 their identification with the chromatin bodies just described 

 as arising in the chromatin reticulum. If now the nuclei of 

 the cells in whose cytoplasm these black spheres lie be examined, 

 it is found either that they contain only a nucleolus and a fine 



