. Text-book of embryology. Embryology. 52 EMBEYOLOGY OF THE LOWEE VEETEBEATES As regards the Birds, which of the higher Anmiotes alone concern us in this volume, there is com- plete agreement that they are to be looked on as highly-special- ized descendants of Eeptilian ancestors. It follows therefore that their develop- mental phenomena should be considered in relation to the cor- responding pheno- mena in Eeptiles. Leaving out of account certain vague phenomena which have been inter- preted, in the present writer's opinion un- justifiably, as remin- iscences of gastrula- tion processes
. Text-book of embryology. Embryology. 52 EMBEYOLOGY OF THE LOWEE VEETEBEATES As regards the Birds, which of the higher Anmiotes alone concern us in this volume, there is com- plete agreement that they are to be looked on as highly-special- ized descendants of Eeptilian ancestors. It follows therefore that their develop- mental phenomena should be considered in relation to the cor- responding pheno- mena in Eeptiles. Leaving out of account certain vague phenomena which have been inter- preted, in the present writer's opinion un- justifiably, as remin- iscences of gastrula- tion processes (see Chapter X.), the for- mation of a gastrular lip seems to have Fig. 32. — Transverse sec- tions through region of neurenterie canal of Ohe- loiiia embryo with about 16 segments. (After Mitsukuri, 1896.) The mid-dorsal ectoderm has become covered in to form the neural tube () as will be de- scribed in Chap. II. Fig. C shows the neurenterie canal opening upwards through this, while Figs. B, D and E, taken from sections anterior and pos- terior to the neurenterie open- ing, show the continuity of tissue from ectoderm to endo- derm which is a characteristic feature of a primitive streak. ect, ectoderm ; end, endoderm ; mes, mesoderm; N, notochord; , neurenterie canal; , spinal 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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