. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. stages of dcveloperaent of the ovarian ctrfe' of a verto- brate animal {continued), clxxvi. to a series of self-si^littings of the impregnated centre, whicli ' fissiparous' j)rogcny assimi- late or incorporate more or less of the yolk. In fig. 4, a, d is the impregnated germ- yolk ; e the fluid between it and the zona, f; f is albumen from which the chorion, cho, arises. In b, fig. 4, is shown the first division or segmen- tation of the germ-yolk; c shows the second division; and D, a later stage in which the 'â ^z^'c^c'
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. stages of dcveloperaent of the ovarian ctrfe' of a verto- brate animal {continued), clxxvi. to a series of self-si^littings of the impregnated centre, whicli ' fissiparous' j)rogcny assimi- late or incorporate more or less of the yolk. In fig. 4, a, d is the impregnated germ- yolk ; e the fluid between it and the zona, f; f is albumen from which the chorion, cho, arises. In b, fig. 4, is shown the first division or segmen- tation of the germ-yolk; c shows the second division; and D, a later stage in which the 'â ^z^'c^c'^^il:^^ properties of the impregnated centre have been diffused and distributed by fissiparous midtiplication 'amongst the countless nucleated cells which form the eerm-mass. Thus far the vertebrate germ resembles in form, structure, and 2 behaviour, the infusorial monad and the germ- stage of invertebrates. The next step impresses upon the nascent being its ' vertebrate' type. Linear rows of the nucleated cells coalesce and become converted into the nervous axis, which under the form or appearance of a double chord, fig. 5, cli, marks the dorsal or ' neural' aspect of the embryonal rudiment. The nutritive organs grow from the opposite side. Along the inter- space is laid the basis of the skeleton, as a gelatinous cylinder, in a membranous sheath, called ' notochord,'' 3 which developes a pair of jjlates ' neurad' ^ to enclose the nervous axis, and a pair of plates ^ hfemad'' to enclose the vascular axis and organs of vegetative life. Flesh and skin coextend with the enclosing plates. This formation of two distinct parallel cavitiesâ' neural' and ' hremal'âunder symmetrical guidance in the vertical or ' neuro-hannal' direction, with a repeti- tion of parts on the right and left sides, establishing transverse or 'bi-latcral'. Spcnii-cclJ, with tlireo spei-matoa, and tinii- nucleus tlie 'spLTmato- zoon'(Cock). Please note that these images are extracted from scanned
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1860
