File:Text-book of comparative anatomy (1898) (14593110870).jpg

Identifier: textbookofcompar01lang (find matches)
Title: Text-book of comparative anatomy
Year: 1898 (1890s)
Authors: Lang, Arnold, 1855-1914 Bernard, Henry Meyners Bernard, Matilda Haeckel, Ernst Heinrich Philipp August, 1834-1919
Subjects: Anatomy, Comparative
Publisher: London, New York, Macmillan and Co.
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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m all sides over the embryonic rudiment,finally covering it. The embryonic rudiment thus comes to lie in the base of a cavitywhose mouth, wide open at first, grows smaller and smaller by the growing and finalclosing together of the amnion folds ; the final closing takes place over the anteriorend of the embryonic rudiment. The tranverse section B, Fig. 350, shows the risingamnion folds, the transverse section C shows them grown over the embryonicrudiment so as to form a continuous cover. In the surface views of Fig. 352 thefolds are denoted by af and of. The cavity which is formed by the amnion is called the amnion cavity. Its roof,in correspondence with its origin, consists of 2 epithelial lamella?, an inner one, whichat the edge of the embryonic rudiment is continued into its blastoderm and representsthe actual amnion, and an outer one, which at the edge of the embryonic rudimentis continued into the blastoderm of the whole remaining surface of the egg, and COMPARATIVE ANATOMY CHAP.
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V/z » s o> *- • -y *j .»>a ffllil .5 i* VI HEXAPODA—EMBRYON 1C DEVELOPMENT 495 together with this represents an unbroken epithelial membrane, the serous envelope ;this latter surrounds the whole egg with its embryonic rudiment and the amnion onall sides. The amnion and the serous envelope have no share in the building up of theembryo. The latter develops exclusively out of the blastoderm of the embryonicrudiment and the invaginated tube, which we will call the germ streak. The blasto-derm of the embryonic rudiment grows further and further dorsally at its peripheraledges, so that at last it envelops the embryo on all sides as ectoderm. Thoughsomewhat out of its strict order, for the sake of clearness, this process as well as thefate of the amnion and serosa may be here illustrated by means of the following dia-gramatic transverse sections. Fig. 351, A, represents the same stage as Fig. 350, F,

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