206 First Maturation Spindle of Allolobophora Foctida 



4, 7, 13, Plate I, 32, 37, 29, 31, Plate II, 49, 50, 58, 60, Plate III, 71, 

 Plato IV), whereas the accessory nucleoli vary in number from one to 

 six or more.' The principal nucleolus is composed of two substances dif- 

 fering in density and producing, though not invariably, the so-called 

 vacuolated appearance, whereas the accessory nucleoli are dense homoge- 

 neous bodies and are, as a rule, not vacuolated. The principal nwlcohis 

 and the accessory nucleoli are clearly seen in unstained sections, even the 

 smallest of the accessory nucleoli appearing homogeneous and refractive. 

 In Photos. 23, 29, 39, 40, Plate II, 56, Plate III, both kinds of 

 nucleoli are shown in the same section of a germinal vesicle. Photos. 

 3 and 4 show two sections of the same germinal vesicle, the former 

 containing the accessory nucleolus and the latter the principal nucleolus. 

 Photos. 6, 7, 8 and 9 are sections of one germinal vesicle, Photos. 7 and 

 8 showing the principal nucleolus and Photos. 6, 8, 9 showing each one 

 accessory nucleolus. After certain fixatives, e. g., platino-osmic, the 

 principal nucleolus stains very faintly with iron heematoxylin and can be 

 readily decolored, whereas the accessory nucleoli retain the hsematoxylin 

 with as much tenacity as do the chromosomes.* The principal nucleolus 

 disappears before the first maturation spindle is formed, whereas the 

 accessory nucleoli often persist as late as the metaphase of the first 

 maturation spindle. They do not always persist, however, until this 

 period, and when they are present, their position is most inconstant, some- 

 , times being within the area of the spindle, even at the equator, but more 

 often in the cytoplasm at different distances from the spindle. The 

 presence of the persisting nucleoli was noted and figured in an earlier 

 paper (Foot, '94), but at that time we had not recognized them as 

 accessory nucleoli but supposed them to be fragments of the large egg 

 nucleolus. 



In unstained sections the so-called vacuoles of the principal nucleolus 

 are entirely transparent and sharply differentiated from the rest of the 

 nucleolus which is dense and refractive (Photos. 14b, 15 to 21, Plate I, 

 35, 39, 40, Plate II, and 74, Plate IV). Stained preparations, however, 



' This applies to sections. In all dried germinal vesicles that appear to be 

 normal, we find as a rule only one accessory nucleolus, though we have some- 

 times found two (Photo. 115, Plate VII), rarely three, and in one or two cases 

 five. Sections of fixed eggs indicate that the single accessory 7iucleolus 

 probably owes its origin to the fusing of several small ones. 



'^ That the principal nucleolus fails to stain readily at these stages when 

 the accessory nucleolus stains very intensely may be due to the disintegra- 

 tion of the former, for at an earlier stage of development the principal nucle- 

 olus stains intensely. 



