24 THE hen's egg, [chap. I. 



than a distinct membrane. Their nuclei are not readily 

 visible. 



At the time when the segmentation-spheres in the 

 centre are smaller than those at the periphery, and 

 those above are also smaller than those below, a few 

 large spherical masses, probably containing each one of 

 the nuclei already spoken of, arise by a process of seg- 

 mentation from the bed of white yolk, and rest directly 

 on the white yolk at the bottom of the shalloAv cavity 

 below the mass of segmentation- spheres. They contain 

 either numerous small spherules, or fine granules ; 

 the spherules precisely resembling the smaller spheres 

 of white yolk. These loose spherical masses form the 

 majority of the formative cells already spoken of. 



Thus the original germinal disc of the ovarian ovum 

 becomes, by the process of segmentation, converted into 

 the blastoderm of the laid egg with its upper layer of 

 columnar nucleated cells, and its lower layer of irregu- 

 larly disposed cells, accompanied by a few stray " forma- 

 tive " cells lying loose in the cavity below. 



