290 THE OVARIAN EGG. 



the side, like the Purkinjean vesicle itself; but it 

 does not retain this position, for, as soon as its 

 wall is formed and it becomes a distinct body, it 

 floats away from the side and takes its place in 

 the centre. Next there arise within it a number 

 of little bodies crystalline in form, and which 

 actually are wax or oil crystals. They increase 

 with great rapidity, the inner sac or mesoblast 

 becoming sometimes so crowded with them that 

 its shape is affected by the protrusion of their 

 angles. This process goes on till all the cells are 

 so filled by the mesoblast, with its myriad brood 

 of cells, that the outer sac or ectoblast becomes a 

 mere halo around it. Then every mesoblast con- 

 tracts ; the contraction deepens till it is divided 

 across in both directions, separating thus into 

 four parts, then into eight, then into sixteen, and 

 so on, till every cell is crowded with hundreds of 

 minute mesoblasts, each containing the indication 

 of a central dot or entoblast. At this period every 

 yolk cell is itself like' a whole yolk ; for each cell 

 is as full of lesser cells as the yolk-bag itself. 



When the mesoblast has become thus infinitely 

 subdivided into hundreds of minute spheres, the 

 ectoblast bursts, and the new generations of cells 

 thus set free collect in that part of the egg where 

 the embryonic disk is to arise. This process of 

 segmentation continues to go on downward till 

 the whole yolk is taken in. These myriad cells 



