In the periphery of the cytoplasm, small vacuoles appear at first, later bejng filled with 

 yolk during the growth of the ovocyte, and moving towards the centre of the cell (Figure 3), 



Figure 3. Ovary of a Murmansk herring, Oct. 14, 1938 near the Karlov Islands, 

 of fish 239 mm., age 5+, stage III, x 100. 



Length 



Single vacuoles lack the yolk globules. The protoplasm is granular. There are many karyo- 

 somes, of an oval-rounded shape, situated close to the cell membrane. In preserved preparations 

 the membrane of the nucleus looks very undulated. The chromosomes resemble "lamp-brushes". 



During further development the yolk globules migrate towards the centre of the egg cell. By 

 degrees they fill most of the cytoplasm. The oval -rounded yolk globules are faintly stained in 

 Heidenhain's hematoxylin. 



Granules of an irregular, cubical shape, appearing in the cytoplasm together with the oval- 

 rounded yolk globules, are an indication of the transition to the following phase (Figure 4). They 

 are coloured intensively black by Heidenhain. This yolk mass is spread by degrees to the centre 

 of the ovocyte, occupying nearly all the space between the nucleus and the membrane. When the 

 formation of cubical yolk is finished, the ovocytes pass over to the next phase. 



The phase of ovocytes filled with yolk . Diameter of the ovocytes 592-736 mu, average 675.2 

 mu. The nucleus has no definite shape, and cannot be measured. As in the foregoing phase, the 

 ovocytes form two layers in the follicle . 



The zona radiata has increased in thickness, 

 is a thin layer of granular protoplasm, free of yolk. 



being very clearly defined. Close to the zone 

 Next comes a small layer with round-oval 



214 



