No. 2.] THE EGG OF BUFO LENTIGINOSUS. 309 



they end apparently in the fine granular network which fills the 

 greater part of the space once occupied by the germinal vesicle, 

 and are beginning to have a radiate appearance. In the suc- 

 ceeding stages, in proportion as the radiation becomes more 

 marked the rays become longer, thicker, more numerous, and 

 from being apparently homogeneous as when first formed, they 

 are seen to consist of a series of minute round microsomes. The 

 granules of nucleoplasm, on the contrary, constantly decrease 

 in size and number and stain less intensely (PI. XXVIII, 

 Fig. 15). When the radiation has reached its greatest extent 

 (PI. XXIX, Fig. 18), every trace of the nuclear granules has 

 disappeared. The change is so marked that it admits of but 

 the one interpretation, that the rays grow at the expense of 

 the granular substance once a part of the germinal vesicle. 



During this period a series of changes has also taken place 

 below the line of radiation. After the withdrawal of the fibers 

 from above, the fine reticulum extending between the coarse 

 granules in this region disappears and the granules themselves 

 break up into smaller ones (PI. XXVIII, Fig. 14, A). At the 

 next stage (PI. XXVIII, Fig. 15), this substance is a uniformly 

 finely granular mass, which stains a light pink and contains a 

 few scattered pigment granules. Meanwhile there has been a 

 gradual movement of the line of radiation, and all the substance 

 formerly contained in the germinal vesicle, towards the upper 

 pole of the ^g^ (PI. XXIX, Fig. 17). This movement must be 

 brought about by some rearrangement in the yolk and cyto- 

 plasm of the Q.gg, as it is inconceivable that these structures 

 can have the power of independent movement. 



Hertwig has figured the germinal vesicle of the frog's Q^g 

 just before its disintegration as a flattened oval structure with 

 a distinct membrane, lying close to the upper surface of the 

 Qgg. As the phenomena which take place during the matura- 

 tion of the Qgg of the frog and toad appear so closely similar 

 in most respects, it seems probable that in the former as well 

 as in the latter the germinal vesicle breaks down some dis- 

 tance below the surface of the &gg. Presumably, therefore, 

 Hertwig's Fig. 7, which shows the germinal vesicle, still sur- 

 rounded by its membrane, lying close to the upper surface of 



