Ultrastructural Studies on Development of the Tail Gland of a Cuttlefish, Sepiella japonica

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Abstract
Hatchine glands in embryos of teleosts and amphibians have been reported to be indispensable for hatching of the embryos. The cephalopod has capsuled eggs, so we expected to find some exocrine organ in the embryos that functioned as a hatching gland. The tail gland (Hoyle''s organ) has been suspected to be a hatching gland in the cephalopod, and therefore we examined it during the course of development of cuttlefish embryos. Cells in the tail gland appeared similar to the hatching gland cells (HGCs) of teleosts and amphibians, and contained a number of secretion granules that also resembled the hatching enzyme granules (HEGs) in HGCs of teleosts and amphibians in size, electron density and distribution in the cells. However, a few of these granules were discharged one after another from an early stages, whereas most of them were retained up to the stage just before hatching, and then discharged all at once. The former process of trickling discharge was similar to that in amphibians and the latter process of abrupt discharge resembled that in teleosts.