AUTHORS ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, OCTOBER 4 



STUDIES ON THE RETINA 



THE STRUCTURE OF THE RETINA OF PHRYNOSOMA CORNUTUM 



S. R. DETWILER AND HENRY LAURENS 



Anatomical Laboratory, School of Medicine, and the Osborn Zoological Laboratory, 



Yale University 



SIX FIGURES 



The retina of lizards and turtles is peculiar in that, with few 

 exceptions, it contains only cones. The Gecko, for example 

 (Rochon-Duvigneaud '17), is a nocturnal animal and the pure 

 rod retina which it possesses represents, in accordance with the 

 suggestion put forward by Max Schultze ('66), a retinal mechan- 

 ism particularly adapted for nocturnal life. According to this 

 widely held view (duplicity theory) pure cone retinae are indica- 

 tive of a diurnal mode of life, and forms possessing this type of 

 retina have little or no capability of vision in dun light. 



This paper will describe the salient histological featm-es of the 

 retina of Phrj^nosoma, and present a review of the literature in 

 so far as it bears upon the structure of the reptilian retina and 

 the general problems of vision pertaining thereto. The retina of 

 Phrynosoma possesses only cones, resembling in this respect the 

 retinae of other diurnal saurians. In its general make-up it may 

 be said to resemble most closely that of Chameleon vulgaris (Gar- 

 ten '07 and Rochon-Duvigneaud '17). 



The most striking features which this' retina exhibits are: a) 

 the absence of rods; b) the presence of a large conical pecten; 

 and c) the presence of a prominent area centralis containing a 

 maxunally developed fovea. A detailed study reveals a number 

 of additional interesting features, the most significant being the 

 shape and structural variableness of the visual elements. 



Chievitz ('89, '90, and '91) described the area centralis in a 

 munber of representative mammals, birds, reptiles, and amphibi- 

 ans. In the reptiles he found an area in lizards, snakes, turtles, 



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