Nucleoli during- the Oogenesis of the Dragon-fly. 217 



The g-erni-cells described in the germinal area are of course 

 the oogonia and one would expect to find here an abundance of 

 oog'onial divisions. Such, however, is not the case, for -wMien the 

 period of rapid growth begins, mitosis is not found in the egg- 

 string. All of the material which was studied was taken at too 

 late a stage to show oogonial divisions. I think it quite probable 

 that this period of division is very short in the dragon-flj-, and that 

 it is to be found only in the very youny larvae. 



Another process of importance in the germinal area is the be- 

 ginning of the formation of the yolk-nuclei. I have not observed 

 this in detail, but the material appears to be favorable for such 

 study. The yolk-nuclei begin as darkly staining granulai- masses 

 lying close against the outer surface of the nuclear membrane 

 (Fig. 2, 7. 12, 14. 39, 41 and 50). Arising, as they do. in such close 

 proximity to the nucleus, it would seem as if there were some 

 transfer of nuclear material, which on reaching the cytoplasm is 

 there deposited. As there is a peripheral layer of chromatin just 

 within the nuclear membrane, it is very easy to imagine that the 

 formation of the yolk-nucleus depends in some way upon this layer 

 of chromatic material. Better proof of this, however, is given by 

 -diiferential stains. When such stains are used, the granules of the 

 yolk-nuclei stain much the same as chromatin. The later develop- 

 ment of these structures will be described in connection with the 

 growth-area of the egg-string. 



3. T h e (if r o w t h A r e a. 



As before stated, it will be necessary to describe the growth- 

 area of Aîiax and Flathemis separately because of the very pro- 

 nounced différence between the nucleoli of these two forms in their 

 later development. 



a) The Growth Area in Plathemis lydia. 



In the growth area of Flathemis. the ova separate from the 

 germinal mass into a string of cells a single cell in thickness and 

 extending in length backwards and outwards to the oviduct. Each 

 ovum is entirely surrounded by a layer of follicle-cells. The are;i 

 in each egg-string contains from twenty to forty ova arranged end 

 to end with their long axes parallel with the long axis of the string. 

 The ova gradually increase in size as they approach the oviduct. 



