74 SEVENTEENTH REPORT. 



greater importauce, they serve to strengthen our faith that the 

 reagents ordinarily used in fixing solutions do not destroy the ob- 

 jects they are intended to reveal. 



Yolk islands. Some material obtained in the fall of 1913 gave 

 preparations which seem to afford direct evidence that the problem- 

 atical bodies seen in living material are not nucleoli and are not 

 even included within the nuclear membrane; they are composed of 

 small masses of yolk that become imprisoned between the vitelline 

 membrane and the germinal vesicle when the latter approaches the 

 surface. For convenience they may be called "yolk islands" (PI. 

 V B). My earlier preparations comprised only a few slides show- 

 ing the germinal vesicle at the surface, and these happened not 

 to have the yolk islands. These objects thus prove to be lacking in 

 theoretical importance, but from a practical point of view it is 

 worth while to have determined their nature in order to eliminate 

 them from further consideration in connection with studies of the 

 germinal vesicle. 



THE RECESSION AND DISSOLUTION OF THE GEORMINAL VESICLE. 



The migration of the germinal vesicle from the center of the egg 

 to the surface at the animal pole has been previously described 

 (Smith, 1912) ; but formerly I was unable to secure the exact 

 stages showing the dissolution of the germinal vesicle. One lot of 

 material preserved during the fall of 1913 gave the stages desired. 



The dissolution of the germinal vesicle does not take place at the 

 very surface of the egg, but the vesicle recedes a not inconsiderable 

 distance before dissolution occurs. During recession a trail of 

 cytoplasm is left between the germinal vesicle and the animal pole. 

 In some eggs the germinal vesicle appears to be in a state of dis- 

 integration without ever having reached the animal pole, as shown 

 by the absence of this trail of cytoplasm. 



The dissolution of the germinal vesicle takes place by a gradual 

 disintegration and convergence of its membrane, rather than by a 

 localized rupture such as would be expected to occur if it burst 

 through pressure from within. During the process the disinteg- 

 i-ating wall becomes thicker and more spongy in nature, and stains 

 more deeply than before. 



In my prei)arations I have found but a single egg showing the 

 germinal vesicle just before the process of dissolution is complete. 

 This egg was stained in toto with paracarmine. The vesicle con- 

 tains, besides some nucleoli, numerous deeply stained spherical or 

 lobed bctdics. resembling nucleoli but much larger and not so regu- 

 lar in form. They may be artifacts, but my inii)ression is that they 



