. Embryology. Embryology; Embryology; genealogy. 70 EMBRYOLOGY us what structures may be derived from the ectoderm when it is placed in new environments. If the ectoderm has the ability to differentiate into a certain structure in a certain environment, the ectoderm is said to possess the potency for the formation of that structure. The potencies of any part may be defined as its abilities to differentiate into various kinds of structures in various kinds of environments. The anatomy of an amphibian embryo In order to make the proposed analysis we must outline the structures present in an earl
. Embryology. Embryology; Embryology; genealogy. 70 EMBRYOLOGY us what structures may be derived from the ectoderm when it is placed in new environments. If the ectoderm has the ability to differentiate into a certain structure in a certain environment, the ectoderm is said to possess the potency for the formation of that structure. The potencies of any part may be defined as its abilities to differentiate into various kinds of structures in various kinds of environments. The anatomy of an amphibian embryo In order to make the proposed analysis we must outline the structures present in an early embryo so that we may recognize them in the results of our experiments. For this purpose a schematic diagram of a longitudinal section is given in Figure 30. These same schematic representations of struc- ture will be used in the analytical part which follows this outline. The brain and spinal cord show regional differences, and we distinguish forebrain, midbrain, hindbrain, and spinal cord. The forebrain forms the optic vesicles, which differentiate into the retina and optic nerve, while the epidermis forms the lens of the eye. Opposite the forebrain the nasal placodes develop; these form the sensory epithelium of the nose. Also near PRONEPHRIC DUCT SPINAL CORD NOTOCHORD HINDBRAIN OTOCYST,. SPLANCHNIC MESODERM FOREBRAIN NASAL PLACODE EPIDERMAL PITUITARY PHARYNX Fig. 30. A highly diagrammatic representation of the structures in the early embryo. The general shape and position of the parts can be recognized in sec- tions of the embryo. The basic plan of all the adult structures is laid down at this 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 Barth, Lester G. (Lester George), 1905-1979. New York, Dryden Press
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