TEN or twelve hours after the commencement of copulation, yolk-granules begin to be deposited on the outer surface of the germ-vesicle, around which they speedily increase in number and form a homogeneous layer, which does not, however, succeed in reaching the vitelline membrane ; albeit that the latter becomes more and more encroached upon from without. Its distinctness may, at any time, be demonstrated by the addition of water or acetic acid; as may also that of the germ-vesicle, even when wholly concealed by its fully formed investment of yolk-substance.

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