128 Transactions of the Society. 



nucleoli however remain distinct throughout the process of yolk 

 formation, but by the time that the yolk bodies are fairly evenly 

 scattered through the cytoplasm, both the oxyphil and basophil 

 bodies have become vacuolated, and they commence to disintegrate. 

 The oxyphil nucleolus breaks up into fragments which pass into 

 the cytoplasm, as is seen taking place in Fig. 11, while the basophil 

 nucleolus disintegrates and spreads out over the linin network of 

 the nucleus. Fig. 12 sliows this process taking place. When the 

 basophil material is spread out in this manner there appears to be 

 a small quantity of oxyphil substance left over, as is seen in 

 Fig. 12 at FO. This seems eventually to pass out into the cyto- 

 plasm. 



The basophil substance becomes spread out evenly over the 

 linin network and forms little bodies at the nodes of the reticulum 

 (FB in Fig. 13), resembling similar structures in the nuclei of 

 somatic cells which are usually described as karyosomes. 



It has been impossible to ascertain accurately whether a small 

 quantity of oxyphil matter does or does not remain in the mature 

 oocyte, owing to the present difficulty of obtaining oocytes at the 

 maturation stages. This problem, together with the subsequent fate 

 of the nucleolus, is still under investigation. 



Discussion. 



It will be noticed from the above description that the oxyphil 

 nucleolus resembles in its general behaviour that of Lihcllula and 

 Periplaneta (S) as described by Hogbeu, in that there is an early 

 extrusion of oxyphil granules from the nucleolus into the cytoplasm. 

 These granules however " pass to the periphery of the oocyte, where 

 they Ijreak up into smaller spheres which become the first vitellus." 

 A somewhat similar process has been described by Gatenby in the 



Plate IV, 



Fig. 9. — Older oocyte with the two parts of the nucleolus separated. Extru- 

 sion is taking place of oxyphil substance which had been left attached to basophil 

 nucleolus. 



Fig. 10. — Oocyte at a later stage with a large vacuolated basophil nucleolus 

 (BB), and a smaU vacuolated oxyphil nucleolus (OB). Yolk spherules (YS) are 

 lairly evenly scattered throughout the cytoplasm. 



Fig. 11. — Older oocyte showing the breaking up and extrusion (FO) of the 

 oxyphil nucleolus and the beginning of the spreading out of the basophil sub- 

 stance (F and FB). 



Fig. 12. — Nucleus showing the disintegration of the basophil nucleolus (DB), 

 and the dispersal of its substance (FB) over the linin network (LN). Oxyphil 

 fcubstance produced as the result of this process is seen at FO. 



Fig. 13. — Nucleus with basophil substance (FB) fairly regularly arranged upon 

 the linin network. At NE is seen some of the remaining oxyphil substance being 

 extruded into the cytoplasm. 



