Ontogeny of vision in the peking duck (Aanas platyrhynchos): The pupillary light reflex as a means for investigating visual onset and development in avian embryos

The pupillary light reflex was used to determine the onset of visual function in Peking duck embryos (Anas platyrhynchos). Neurally mediated pupillary responses were first elicited on Day 18 (67% of total incubation), but 2 days prior to this and for several days during prenatal life, autonomous iris constriction was found. The neural and nonneural components of the response were separated using both an excision and a curare technique, each of which produced similar results. The pupillary technique for studying visual onset and development was further evaluated by a study of chick embryos (Gallus gallus), in which it was seen that results from this technique were in good agreement with those gleaned from more complex methods. It was concluded that the technique affords several advantages, particularly with respect to clarity of interpretation, ease of execution, and amount of information provided.