. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. METAMERISM 541 derm is complete dorso-ventrally, including the hypomeric region of the mesoderm. It becomes evident, therefore, that the suppression of segmentation in the hypomeric area in the vertebrate embryo achieves a precocious result which the embryo of Amphioxus reaches only at a later period of develop- ment. Presumably in the vertebrate embryo, segmentation of the epimeric mesoderm is retained because it serves a definite end, whereas se
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. METAMERISM 541 derm is complete dorso-ventrally, including the hypomeric region of the mesoderm. It becomes evident, therefore, that the suppression of segmentation in the hypomeric area in the vertebrate embryo achieves a precocious result which the embryo of Amphioxus reaches only at a later period of develop- ment. Presumably in the vertebrate embryo, segmentation of the epimeric mesoderm is retained because it serves a definite end, whereas segmentation of the hypomeric mesoderm is deleted because it also leads to a necessary end result in a direct manner. When applied to the developing head region, this procedure principle means this: A primitive type of segmentation does tend to appear in the pre-otic area as well as in the post-otic portion of the head, as indicated by the pre-otic and post-otic somites, and secondarily there is developed a branchial metam- GASSEF1I4N GSNGLION OF NERVE T METENCEPHl GENICULATE GANGLION OF NERVE SH. ACOUSTIC GANGLION OF NERVE TTTTT MTELENCEPHAL OTIC VESICLE SUPERIOR GANGLION OF NERVE H JUGULAR GANGLION OF NERVE I PETROSAL GANGLION ( NERV NODOSE GANGLION 0. Fig. 259. Chick embryo reconstruction of about 100 hrs. of incubation with special reference to the nervous and urinary systems. See also fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nelsen, Olin E. (Olin Everett), b. 1898. New York, Blakiston
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