Accommodation and Its Reflex Pathways in the Teleosts *

The problem of vision in the fishes has occupied the attention of investigators for over a century and a half. The observations of naturalists, experimentalists, and morphologists and the conclusions drawn by them have not been in agreement because many of them have failed to consider all factors influencing the formation of an accurate and clear retinal image, and, also, to realize that all fishes may not have or need equally good vision. Numerous amazing stories which speak for remarkable vision may be found in the literature. Perhaps no evidence is so striking as that offered by the East Indian archer-fish (Toxotes) which, after maneuvering into position, can throw a fluid projectile three to five feet above the water to hit accurately its insect prey.t Such ability is even more astounding when one considers that this marksmanship takes into account the refraction of light rays at the surface of the water. The existence of visual acuity and localization is also suggested in the terrestrial habits of the climbing perch (Anabas) and the walking goby (Periophthalmus) in their search for food, in the mating reaction of the male guppy (Lebistes) described by Breder and Coates3, as well as in the less bizarre habits of many other fishes. Its existence is likewise suggested by the morphological and physiological evidence available. Sharpness and range of vision are dependent upon the external factors of the environment, such as the density of the medium, the dispersion of the light rays, the intensity of the light source, the turbidity of the water, etc., as well as upon the degree of development and the physiological activity of the structures for the perception of light and for focussing light rays. These latter intrinsic factors include the number and types of visual elements in the retina and the adequacy of the mechanism of accommodation. In general,