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 
