author's abstract of this paper issued 

 by the bibliographic service, mat 1 



A RETINAL MECHANISM OF EFFICIENT VISION^ 



LESLIE B. AREY 



The Anatomical Laboratory of the Northwestern University Medical School 



TWO TEXT FIGURES 



PRELIMINARY 



It is a well-established fact of retinal physiology that the 

 visual cells and retinal pigment in many of the lower vertebrates 

 exhibit striking movements in light and in darkness ('15 a, '16), 

 although in man and other mammals such changes apparently 

 are slight ('15 b). 



The pigment cells have processes, probably fixed, which inter- 

 digitate with the visual elements and in which the pigment 

 granules migrate to and fro (figs. 1 and 2). The visual cells 

 likewise modify their positions due to the contractility of the 

 so-called myoid, which is that portion of the inner member of 

 the rod or cone between the ellipsoid and the external limiting 

 membrane. The extensibility of the myoid is variously de- 

 veloped, but in some animals the extremes of change may be as 

 one is to ten ('16). 



There is represented in figures 1 and 2 the condition of the 

 retina, with respect to these changes, as it is characteristically 

 found in a fish, the common horned pout, Ameiurus. In dark- 

 ness (fig. 1) the pigment withdraws toward the chorioid, thus 

 exposing the visual rods and cones; of the two types of visual 

 elements the cone is extended, whereas the rod is so retracted 

 that its ellipsoid lies close to the external limiting membrane. 

 In light (fig. 2) the appearance is reversed; the pigment now 



1 Contribution No. 69, March 3, 1919. The experimental data were obtained 

 at the Fairport Biological Station while a guest of the United States Bureau of 

 Fisheries. 



343 



