The embryological development of primary visual centres in the turtle Emys orbicularis

The development of the primary visual centres was studied in a series of embryos of the turtle, Emys orbicularis, incubated at 25 degrees C. The differentiation of both visual and nonvisual diencephalic and mesencephalic structures takes place entirely within the 2nd quarter of the period of incubat...

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Bibliographic Details
Published in:Journal of anatomy 1993-10, Vol.183 (Pt 2), p.367-404
Main Authors: HERGUETA, S, LEMIRE, M, PIEAU, C, WARD, R, REPERANT, J
Format: Article
Language:English
Subjects:
Animals
Biological and medical sciences
Brain - anatomy & histology
Brain - embryology
Embryology: invertebrates and vertebrates. Teratology
Fundamental and applied biological sciences. Psychology
Hypothalamus - anatomy & histology
Hypothalamus - embryology
Mesencephalon - anatomy & histology
Mesencephalon - embryology
Organogenesis. Fetal development
Organogenesis. Physiological fonctions
Superior Colliculi - anatomy & histology
Superior Colliculi - embryology
Thalamus - anatomy & histology
Thalamus - embryology
Turtles - anatomy & histology
Turtles - embryology
Vision, Ocular - physiology
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Summary:The development of the primary visual centres was studied in a series of embryos of the turtle, Emys orbicularis, incubated at 25 degrees C. The differentiation of both visual and nonvisual diencephalic and mesencephalic structures takes place entirely within the 2nd quarter of the period of incubation; this finding appears to be consistent with previous descriptions of the embryology of 2 other chelonian species, Lepidochelys and Chelydra. Two successive waves of migration, each dividing into internal and external sheaves, are involved in the formation of the structures of the diencephalon and mesencephalon. The primary visual centres, which comprise 2 hypothalamic, 5 thalamic and 5 pretectal zones of retinal projections, together with the 2 superficial layers of the tectum and a single tegmental projection zone, all have their origin in the external sheaf of the 1st wave of migration. The finding that the adult nucleus geniculatus lateralis dorsalis, pars ventralis arises from one of the migrations of the dorsal thalamus is discussed in the context of the debate over the possible homologues of the mammalian geniculostriate visual pathway.
ISSN:0021-8782
1469-7580