Developing visual function in the red jungle fowl embryo.

The onset of visual system function in the wild red jungle fowl embryo was measured by the pupillary reflex technique and compared with its domesticated descendant, the domestic chick. The first neurally mediated pupillary reflex in the jungle fowl embryos was found at Day 15 of incubation after 77% of incubation was completed. This point did not differ significantly from the onset of this reflex in the domestic chick embryo (after approximately 83% of incubation). Thus, it was concluded that the relatively late onset of overt visual system function in the chick, as compared with several other precocial avian species, was not a result of its history of intense domestication but rather was most likely a normal characteristic of this and other closely related species.