th a flattened basal surface ; and since thej do not 



come into close contact with one another at the centre, thej 



iclose between them a cavity (cleavagt> cavity) open above 



id below. With the next act of cleavat^'e each of these four 



Is is divided into two equal parts by a new meridional 



irrow (Fig. 1 G and D) . The embryo now consists of a circle 



C / 



Fig, 2.— Cleavage stages of Sycandra raphanus (after F. E. Schulze). A, two- 

 3II stage ; B, four-cell stage ; C eight-cell stage ; B, the same in vertical section in 

 Its relation to the collared epithelium of the maternal radial tube (diagram) ; E, 

 ixteen-cell stage ; F, the same in vertical section (diagram) ; G later stage of 

 leavage with eight granular (ectodermal) cells at the lower pole ; H, blastosphere 

 Stage in side view. In the interior the cleavage cavity j granular cells below, 

 lerwise an epithelium of tall columnar cells. 



