21ic Behaviour of the Nucleolus during Oogenesis. 127 



the early extrusion of nucleolar material takes place when the 

 nucleus is largest in proportion to the volume of the cytoplasm. 



At the end of the preliminary growth stages the nucleolus 

 becomes rounded off, and a distinct separation into two parts is 

 noticeable. This is shown in the cell drawn in Fig. 5. From this 

 stage onwards the two parts of the nucleolus react differently to 

 stains. One part of the nucleolus (OP) still stains oxyphil, while 

 the other gradually changes. At first, as shown at BP in Figs. C) 

 and 7, it stains a reddish purple, the colour change gradually 

 spreads over the whole of this part of the nucleolus, and it 

 becomes more and more bluish till eventually it appears as a 

 definite basophil body, as is shown at BP in Fig. 8. The nucleolus 

 then appears to be made up of two parts, one the oxyphil body, 

 the other the basophil. 



During the process of differentiation into two parts there seems 

 always to be an extrusion of oxyphil substance into the cytoplasm. 

 This is shown specially strikingly in Fig. 7, where the nucleolus 

 is lobulated and oxyphil fragments are breaking away from it and 

 passing out through the nuclear membrane into the cytoplasm. 

 The nuclear membrane does not appear to be damaged by this 

 process, which recalls the passage of leucocytes through the walls 

 of blood capillaries. The oxyphil portion of the nucleolus during 

 this process is usually vacuolated. 



By comparing preparations fixed in corrosive acetic with those 

 made by osmium tetroxide fixation (e.g. Mann-Kopsch-Altmann 

 technique), it is seen that the early extrusion of nucleolar substance 

 takes place before the dispersion of the Golgi elements, and the 

 latter process commences about the time that the nucleolus becomes 

 differentiated into oxyphil and basophil portions. Such comparisons 

 lead one to assume that the oxyphil material dissolves in the 

 cytoplasm and plays some part in preparing the cytoplasm for the 

 activities of the Golgi elements, which, it was shown in a previous 

 paper {11), are responsible for the formation of yolk spherules. 

 Whether or not this be the case, the nucleolar extrusion ceases for 

 a time, and is not so pronounced from this point onwards, until the 

 end of the odgenetic process. 



After the differentiation of the two parts of the nucleolus, the 

 oxyphil and basophil portions may break up into several smaller 

 bodies, or the two parts may remain joined, or they may separate 

 and form distinct basophil and oxyphil nucleoli. The latter seems 

 to be the commonest occurrence, and in such cases very often there 

 is found a small portion of oxyphil substance remaining attached 

 to the basophil body. 



From the differentiation stage onwards, the oxyphil part of the 

 nucleolus becomes gradually smaller in proportion to the basophil 

 portion, and a certain amount of extrusion of oxyphil substance 

 goes on. This is seen by comparing Figs. 9 and 10. The two 



