| Summary: | In fishes which have pelagic ova and an annual spawning season, the formation of yolk in the developing ova to be shed at a given spawning season commences some months after the close of the preceding spawning season. The active development of the annual crop of ova does not take much more than six months. The formation of yolk always commences near the surface of the cytoplasm and extends inwards. In those eggs which develop separate oil globules, a few of these of small size are present long before the formation of yolk commences. The eggs of the mackerel form an exception to this statement. In immature specimens of sole, turbot, brill, &c., examined during the spawning season, the largest ova in the ovaries are found to contain scattered oil globules, and these are also present in the largest transparent ova in spent ovaries of these species. When the formation of yolk takes place in such eggs the oil globules form a zone internal to that of the yolk. The essential peculiarity of the spent ovary is the presence in it of the ruptured follicles, from which the ripe eggs have escaped. The follicular epithelium in these appears to disintegrate and dissolve. The cavity is obliterated by the contraction of the follicle, which forms a mass of cells and fibres, and is finally absorbed soon after the commencement of the formation of yolk in the eggs for the following season. In the spent ovary there are a number of eggs which have not reached the ripe condition, which die, and are not discharged from their follicles, but absorbed in situ. In the fresh state they are visible as opaque amorphous masses. Similar opaque masses are also seen in immature ovaries in which spawning has never occurred. Here also they are aborted dead ova, which are undergoing disintegration and absorption. They are scattered singly in the ovarian tissue, and their development is arrested at an early stage, before the formation of yolk has made any progress, if even it has commenced. In those in which death has only recently occurred the ...
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