. Sur l'anatomie des vertébrés. L'anatomie comparée des vertébrés ;, ; 1866. Développement d'BATEACIIIA. 621 segments. En b, la constriction de l'utérus commence à définir la tête du tronc : l'ensemble de la coalescence de l'myelonal tracts oblitère la trace linéaire du sillon médian, et le neurapophysial la frontière rudiments myelon. L'embryon et son œuf-masse sont séparés de l'chorion par un liquide clair ; et dans les étapes de l'devehjpement compris épithélium cilié commence à agir sur le fluide dans le sens indiqué par les flèches, l'arrière et d'instance

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. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. DEVELOPEMENT OF BATEACIIIA. 621 segments. In b, the cervical constriction begins to define the head from the trunk : the complete coalescence of the myelonal tracts obliterates the linear trace of the median furrow, and the neurapophysial rudiments border the myelon. The embryo and its supporting yolk-mass are separated from the chorion by a clear fluid ; and in the above-figured stages of devehjpement the ciliated epithelium begins to act upon the fluid in the direction indicated by the arrows, proceeding backward and downward along the sides: the currents are strongest on the hasmal arches, from which the branchlaj are about to be developed. In the mass of em- bryonal cells Ijetwecn the cephalic enlargement of the embryo and the yolk, the heart, fig. 4.31, r, is formed, which becomes hollow, and pulsates before the red blood appears; when the communication with the system of vessels is established, the heart propels blood, at first pale and with spherical corpuscles, in channels formed by liquefaction of cells in the blastema of the second ha3mal arch; and these primary vascular arches esta- blish the communication with the longitudinal aortic trunk simi- larly formed along the under part of the notoehord. The blood returns by venous channels along the yolk, now progressively becoming inclosed by the lateral intestinal plates, and the simple clrcnlatlon is complete. From the substance around the vascular arches are formed as many branchial arches, as subordinate developcmeuts from the second primary hfcmal or visceral arch; and from the branchial arches are budded the succession of vascular loops and coextended ciliated integument, constitutlnjr the outer irills on each side of the batrachian larva, fig. 430. In the magnified portion of the gill, c, the arrows indicate the direction of the ciliary currents. Soon after the ap- pearance of the heart, and of the arches which encompass the primi

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• bookauthorowenrichard18041892
• bookcentury1800
• bookdecade1860