File:Image from page 644 of "On the anatomy of vertebrates (electronic resource)" (1866) (14732641386).jpg

Identifier: b20416039_001 Title: On the anatomy of vertebrates [electronic resource] Year: 1866 (1860s) Authors: Owen, Richard, 1804-1892 Subjects: Anatomy, Comparative Vertebrates Fishes Reptiles Mammals Birds Publisher: London : Longmans, Green Contributing Library: Wellcome Library Digitizing Sponsor: Wellcome Library

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Text Appearing Before Image: In the Skate, fig. 419,A, it is an oblong quad-rangular flattened case,with the angles producedforward and backward,like those of a butcherstray. In the SpottedDog-fish, ib. B, the ovaare also quadrangular,but longer, and the anglesare extended into filamen- FECUNDATION IN FISHES. 599

Text Appearing After Image: The structure and formation of the ovum in scaled and scutedReptiles are essentially the same as in the cartilaginous Fishes.The germ-cell, with a single nucleus, is first formed in a delicateovisac imbedded in the stroma of a solid ovarium. A yolk oflarge size is added, of whichthe greater part consists of 420large non-nucleated oil-vesi-cles, and the smaller partof the vitelline granules andcells with a granulated nu-cleus; these originally sur-round the germ-cell, thenindicate its tract from thecentre to the periphery ofthe yolk, and form with thematter of the germ-cell thecicatricula, or blastoderm.This occupies a much smallerextent of the surface of theyolk than in the small-yolked eggs of Batrachiansand Osseous Fishes, andsegmentation is limited thereto, the rest of the yolk being nutritive. The ovum, con-sisting of the above parts, inclosed in a vitelline membrane, quitsthe ovary and is received into the oviduct: here it acquires acertain proportion of soft albumen, upon which

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