98 BERTRAM G. SMITH 



The first indication of the approach of the germinal vesicle 

 to the surface is the appearance of a faint dark spot, 1 to 2 mm. in 

 diameter, in the center of the blastodisc. This dark spot grows 

 more distinct; it is the optical effect of the scarcely-submerged 

 germinal vesicle. Within this large dark area appears a small 

 sharply defined much darker area, circular in outline, which 

 grows at the expense of the larger and fainter dark area. At the 

 time of its first appearance the small dark area is sometimes seen 

 to pulsate slowly, quiver and change form, disappear and reap- 

 pear. This small dark spot is a portion of the germinal vesicle 

 which is actually in contact with the zona radiata (see section 

 V) . It may increase in size until almost an entire hemisphere of 

 the germinal vesicle is exposed. In light of moderate intensity 

 the germinal vesicle appears as a deep, dark well of transparent 

 substance walled in by the opaque material of the blastodisc; 

 in strong sunlight one may see within the germinal vesicle the 

 reflection of the bright yellow yolk beneath. Several opaque- 

 white bodies of various sizes appear within the germinal vesicle; 

 these are probably nucleoli, though the largest ones are much larger 

 than the nucleoli shown in sections. 



An ovarian egg dissected out and immersed in water at the time 

 of the appearance of the germinal vesicle at the surface orients 

 itself with the animal pole upward. 



The actual disappearance of the germinal vesicle from the 

 surface, and the relation of this process to the rupture of the 

 nuclear wall, have not been satisfactorily observed. Whether the 

 germinal vesicle recedes slightly from the surface before or during 

 the rupture of its wall, or disintegrates at the very surface, has 

 not been positively established; it is possible that all three con- 

 ditions occur in different eggs. In several cases there seemed 

 to be a welling-up of material from the germinal vesicle which 

 spread out to form a broad crater at the surface ; in other cases the 

 appearances favored the impression of a slight subsidence of the 

 germinal vesicle. It is possible that the egg has never been ob- 

 served at the exact time of the rupture of the nuclear wall, for 

 though a large number of eggs from ovaries containing eggs with 



