124 Transactions of the Society. 



complicated case of nucleolar extrusion. " The nucleolus buds off 

 fragments which, passing into the cytoplasm, give rise by fission 

 to numberless granules of a dense proteid nature ; these granules 

 form the main bulk of the reserve material of the Saccocirrus egg 

 and constitute the yolk." 



The behaviour of that part of the nucleolus which remains within 

 the nucleus until the end of oogenesis varies in different animals. 

 In many cases it seems to persist as a definite body until the 

 chromosomes reappear, and then it disintegrates with the breaking 

 down of the nuclear membrane preparatory to the maturation 

 divisions. Kuhn {10), however, describes in Baphnia a large 

 central nucleolus which breaks up to form a number of smaller 

 granules which become spread over the linin network. At the 

 late diakinetic stage when the nuclear membrane breaks down, 

 the remaining nuclear mass disintegrates. Jorgensen (9) working 

 on a species of Patella describes, in the youngest oocytes, a nucleolus 



EXPLANATION OF PLATES SHOWING THE BEHAVIOUE 

 • OP THE NUCLEOLUS IN PATELLA. 



Lettering. — BB. , basophil body or basophil staining nucleolus ; BP., part of nu- 

 cleolus which will form the basophil body ; DB., disintegrating basophil nucleolus ; 

 FB., fragment of basophil substance derived from the basophil nucleolus ; FO., 

 fragment of oxyphil substance derived from the oxyphil nucleolus ; GA., Golgi 

 apparatus; LN., linin network of nucleus; NC, nurse ceU ; NE., oxyphil sub- 

 stance extruded from nucleolus ; NL., nucleolus; OB., oxyphil body or oxyphil 

 nucleolus; OC, oocyte; OP., part of nucleolus which will form the oxyphil 

 body; OS., oxyphil substance remaining attached to basophil nucleolus; T., 

 trabecula wall ; YS., yolk spherule. 



The oxyphil nucleolus and the substance extruded from it into the cytoplasm 

 are shown in red ; the basophil nucleolus in black. The chromophilitj" of the 

 cytoplasm is not represented in colour owing to the difficulty of reproducing the 

 gradations in colour between primary oxyphilia and basophilia, and basophilia 

 and secondary oxyphilia. 



All the figures are drawn from portions of the ovary fixed in either Bouin with 

 acetic or corrosive acetic and stained wich Mann's methyl blue eosin. 



Plate III. 



Fig. 1. — Connective tissue cells, showing the oxyphil nucleolus (NL). 



Fig. 2. — Portion of trabecula, showing young oocyte (00) with oxyphil 

 nucleolus (NL), surrounded by yolk cells. 



Fig. 3.— Older oocyte with a large pear-shaped oxyphil nucleolus (NL) and 

 extruded oxyphil substance in the cytoplasm. 



Fig. 4. — 05cyte at a later stage with nucleolus (NL) rounded ofi and extruded 

 nucleolar material (NE) in the cytoplasm. 



Fig. 5. — An early stage in the differentiation of the nucleolus into two parts. 

 BP will become the basophil body, OP the oxyphil one. 



Fig. 6. — Oocyte during the process of differentiation, showing the extrusion 

 of oxyphil material from the nucleus (NE) and the beginning of basophilia at BP. 



i ig. 7. — A slightly later stage than Fig. 6. The basophilia of BP is more pro- 

 nounced, and the nucleolar extrusion is still proceeding. 



Fig. 8. — Oocyte with distinct oxyphil (OB) and basophil (BB) nucleolar bodies 

 joined together. 



