This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...embryonic formation of this organ which is of such importance for the comprehension of the Cephalopodan body, we are unfortunately restricted to those forms in which it no longer attains full development. Only in a few recent Cephalopods such as Nautilus and Spiriila is the shell It is very questionable if the shell of ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...embryonic formation of this organ which is of such importance for the comprehension of the Cephalopodan body, we are unfortunately restricted to those forms in which it no longer attains full development. Only in a few recent Cephalopods such as Nautilus and Spiriila is the shell It is very questionable if the shell of Spiruia can be regarded as perfect; it is almost internal and evidently much reduced.--Ed. found in its perfect form, and the development of these rare animals is not known. The shell of Argonauta exemplifies other conditions which will be discussed later (p. 294). In those recent Cephalopods in which the development of the shell has been investigated, it lies, enclosed in the mantle (and is thus internal) on the antero-dorsal surface of the body, and either develops into the so-called pen, of a horny character (Om ma xl rephes, Loligo, and others) or consists of numerous calcareous layers built upon a horny foundation (Sepia). It forms in an invagination of the ectoderm, the shell-gland. In a very early embryonic period, a depression appears at the centre of the mantle-rudiment, this being the first indication of the shell-gland (Figs. 115, 116, p. 255, Fig. 131 D, p. 280). At first, in Loligo, this is a wide, shallow pit, but the margin of the pit soon grows inwards and constricts its aperture, the pit finally assuming the form of a sac connected with the exterior by a small opening. This sac is lined with an epithelium composed of cells which, at its base, are specially long, and is surrounded by mesodermal tissue. The aperture of invagination completely closes at a later stage, and the shell-gland then lies internally as a closed sac, surrounded by the mesodermal tissue (Fig. 132 C). It extends later especially anteriorly and then occupie...
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PLEASE NOTE, WE DO NOT SHIP TO DENMARK. New Book. Shipped from UK in 4 to 14 days. Established seller since 2000. Please note we cannot offer an expedited shipping service from the UK.