The vertebrate cornea is an important refractive medium in air, but under water it does not have this function since its refractive index is similar to that of water.The problem of accommodation in amphibious vertebrates has been investigated in a number of species, and Walls ('42) reviews various means by which clear vision is obtained both i n air and in water in a number of vertebrates. For birds, amphibious vision has been studied in cormorants by Iless ('12), in diving ducks, alcids, loons, and grebes by Ischreyt ('12a, b, c, 'l4), and in a species of kingfisher by Xolmer ('24). A group of amphibious birds which had not been studied in this regard were the dippers or water ouzels, a genus of passerine birds inhabiting mountain streams and thought to be most closely related to thrushes or wrens. Consequently, vision and the structure of the eye were included in a study of aquatic modifications in the North American species, Cinclus mexicanus, and this paper describes that portion of the work.The behavior of dippers indicates that they have clear vision both in air and under water. In order to obtain more conclusive evidence for this, a study of refraction in the eye of living birds was undertaken by means of retinoscopy. Refraction of the eye i n air and under water was carried out, and through artificial stimulation the potential range of accommodation was measured.A histological study of the eye of Cinclus was made in a n attempt to identify structural modifications that may be related to amphibious vision. A careful comparative study of the eyes of Cinclus and the non-aquatic Robin ( T u r d u s migratori u s ) , Varied Thrush (lxoreus naevius),and House Wren (Troglodytes aedon) was also made. Since the eye of birds in general has been well described, only structures of special interest and those thought to have a role in the mechanism of accommodation will be considered. The works of Canfield (1886), Franz ('34), Walls ('42), and Rochon-Duvigneaud ('43) contain good general descriptions of the avian eye. The only comprehensive treatment of the eye of an individual passerine species is that of Slonaker ('18) for the House Sparrow (Passer domesticus).The major results of the present study have appeared in abstract form (Goodge, '58) MATERIALS AND METHODSThe refractive state of the eye of three living dippers, one Robin, and one Varied Thrush was determined by the use of a National illuminated retinoscope and a set of test lenses. With the bird held in a frame which prevented movements of its head, the point o€ reversal was measured when lenses from one to 12 diopters were placed in front of the bird's eye.Accommodation was induced by electrical stimulation or by the application of a 0.5% nicotine sulfate solution to the surface of the eye. For the histological work, 8 eyes of Cinclus, and two each of Turdus, Ixoreus, and Troglodytes were fixed in Bouin's or Zenker's solutions. Those fixed in Zenker's solution were placed in Kol-1 Based mainly on a portion of a thesis submitted in partial fulfillment of th...
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