The Behaviour of the Nucleolus during Oogenesis. 129 



case of Saccocirrus {G), where there is an amphinucleoliis with 

 basophil preponderance in the youngest oocytes. From this 

 nucleohis portions break away and pass through the nuclear 

 membrane, remaining attached for a time to its outer surface. A 

 basophil cloud at this stage appears round the nuclear membrane 

 and conceals somewhot the extrusions. This corresponds with a 

 change in the chromophility of the cytoplasm from primary 

 oxyphilia to basophilia. The basophil cloud disperses and the 

 nucleolar granules become arranged spherically around the nucleus. 

 Later they become scattered irregularly in the cytoplasm, and 

 Gatenby shows that by fission they give rise to smaller granules 

 which grow into yolk spherules. In the oocyte of Saccocirrus there 

 are also present small yolk bodies derived from the Golgi apparatus. 



The chief difference between these cases and that of Patella 

 is that in the latter the nucleolar extrusions appear to dissolve in 

 the cytoplasm, and it seems most probable that this dissolved 

 nucleolar substance either becomes converted into yolk under the 

 influence of the Golgi elements, or else acts as an enzyme during 

 yolk formation. This is borne out by the fact that there is always 

 considerable nucleolar extrusion before the Golgi elements spread 

 out in the cytoplasm to form the yolk granules. 



In the oocytes of Ascidians, according to Hirschler (7), there are 

 present densely sUining granules which give rise both to 

 mitochondria and to a yolk nucleus. While the mitochondria are 

 breaking away and spreading out in the oocyte, the densely staining 

 granule is temporarily connected with the nucleus by a stalk along 

 which granules appear to flow out from the nucleus. The yolk 

 granules of Ascidians are complex bodies formed as the result of 

 the fusion of a Golgi element and a swollen mitochondrium, so 

 that it may be that the mitocliondria in these cases contain a 

 small quantity of nucleolar substance, and this functions as an 

 enzyme in the formation of yolk under the joint influence of 

 mitochondria and Golgi elements. 



The chromophility of the cytoplasm of the Ascidian oocytes 

 undergoes two changes. At first, during the primary diffused stage 

 of the Golgi apparatus, the cytoplasm stains oxyphil. When the 

 Golgi elements come together to form a compact body the cyto- 

 plasm becomes basophil, and the change to secondary oxyphilia is 

 concurrent ■ with the scattering oL the Golgi elements, and the 

 formation of yolk from them and the mitochondria. In Patella 

 the Golgi apparatus is compact in the youngest oocytes, and the 

 change from primary oxyphilia to basophilia is unrelated to any 

 observable change in the apparatus. The transition from basophilia 

 to oxyphilia seems to take place at the same time as the fission 

 and spread of the mitochondria, and this occurs after the early 

 nucleolar extrusion has taken place and the nucleolus has been 

 differentiated into oxyphil and basophil portions. 



