298 GEORGE W. BARTELMEZ 



29) also shows the blastodisc regions, and in adjoining sections 

 a broad connection can be traced between the central periblast 

 and the latebra. The photograph shows an additional feature: 

 just below the peripheral protoplasm is a layer of deeply staining 

 granules, (wdg.) extending from the marginal periblast to the 

 germinal vesicle {g. v.). This layer of granules appears wedge 

 shaped in sections of later stages and will be referred to as the 

 'wedge' (wdg.), although actually it forms a broad collar, thicker 

 peripherally, about the germinal vesicle. The granules of the 

 wedge are characterized by being somewhat larger than the neigh- 

 boring granules and by their strong affinity for basic dyes. xVt 

 its central margin the wedge is continuous with a layer of basic- 

 staining but much smaller granules which form a thin stratum 

 over the germinal vesicle except at its outer edge where they form 

 a thickened rim. From their subsequent relations these have 

 been termed the polar granules (fig. 29, p. g.). Both groups can 

 be traced through the succeeding stages, and during maturation 

 and fertilization they are shifted about by cytoplasmic currents 

 so as to form configurations which are among the clearest evi- 

 dences of the bilateral organization of the blastodisc. These 

 granules take the violet in the neutral gentian stain as intensely 

 as do the nucleoli and the granulations within the yolk spheres, 

 differing in this respect from the rest of the granules of the 

 blastodisc, as appears clearly in figures 29 and 30, 40 and 41. 



B. The blastodisc during maturation and first cleavage 



For lack of space at the present time the detailed description 

 of the succeeding stages must be reserved for a later publication. 

 The evidences of bilaterality in these stages are essential for the 

 general thesis here maintained and will be briefly summarized. 

 About two days before ovulation the periblastic zones which 

 characterize the mature egg are established, first posteriorly, then 

 anteriorly. A surface view of a blastodisc in this stage is shown 

 in figure 42. This is the first direct morphological evidence that 

 the blastodisc of the oocyte is bilaterally organized. It shows 

 beyond question that the embryonic axis as such exists in the 

 ovarian egg and establishes the validity of the reasoning from the 



