Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . § 466. Towards the thirteenth day we see a transparent,cartilaginous cord, in the place afterwards occupied by theback-bone, composed of large cells, in which transverse di-visions are successively forming (figs. 306, 307, c]. This isthe dorsal cord, a part of which, as we have before seen, iscommon to all embryos of the vertebrated animals. It alwaysprecedes the formation of the back-bone ; and in some fishes,as the sturgeon (fig. 374),
Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges . § 466. Towards the thirteenth day we see a transparent,cartilaginous cord, in the place afterwards occupied by theback-bone, composed of large cells, in which transverse di-visions are successively forming (figs. 306, 307, c]. This isthe dorsal cord, a part of which, as we have before seen, iscommon to all embryos of the vertebrated animals. It alwaysprecedes the formation of the back-bone ; and in some fishes,as the sturgeon (fig. 374), this cartilaginous or embryonic stateis permanent through life, and no true back-bone is ever after, the first rudiments of the eye appear, in the formof a fold in the external membrane of the germ, in which thecrystalline lens (fig. 307, x) is afterwards formed. At the sametime we see at the posterior part of the head an elliptical vesicle, DEVELOPMENT OF THE YOUNG WITHIN THE EGG. LSf) which is the rudiment of the ear. At this period, the dis-tinction between the upper and the lower layer of the germ isbest traced ; all the changes menti
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1870
