356 S. R. DETWILER AND HENRY LAURENS 



3. A highly vascular conical pecten projects dorso-anteriorly 

 about 1 mm. into the posterior chamber of the eye (figs. 1 and 4). 



4. The retina possesses only cones, resembling in this respect 

 the retinae of other diurnal saurians. The cones exhibit a con- 

 siderable variation in size, shape, and structure (figs. 4 and 6). 



5. The cones of the fovea are greatly attenuated and cylindri- 

 cal in form as compared with the conical form of those in the 

 extra-foveal region (cf. figs. 4 and 5). The presence of double 

 cones could not be demonstrated. 



6. The pigment under ordinary conditions of illumination 

 extends down over the visual cells, almost to the paraboloids 

 (fig. 5) except in the foveal region, where only the outer segments 

 are covered (fig. 3). 



LITERATURE CITED 



Chievitz, J. H, 1889 Untersuchungen liber die Area centralis retinae. Arch, 

 f. Anat. (u. Physiol.), S. 13&-196. 



1890 Untersuchungen liber die Entwickelung der Area and Fovea 

 centralis retinae. Arch. f. Anat. (u. Physiol.), S. 332-366. 



1891 Ueber das Vorkommen der Area centralis retii^ae in den vier 

 hoheren Wirbelthierklassen. Arch. f. Anat. (u. Physiol.), S. 311-334. 



Detwiler, S. R. 1916 The effect of light on the retina of the tortoise and the 



lizard. Jour. Exp. Zool., vol. 20, pp. 165-191. 

 Gakten, S. 1907 Die Veranderungen der Netzhaut durch Licht. Graefe- 



Saemisch Handb. d. Augenheilk., Teil 1, Bd. 3, Kap. 12, Anhang, 2. 



Aufl., 250 S. 

 Heinemann, C. 1877 Beitrage zur Anatomic der Retina. Arch. f. mikros. 



Anat., Bd. 14, S. 409-441. 

 Latjbens, H. and Detwiler, S. R. 1920 Studies on the retina. The structure 



of the retina of Alligator mississippiensis and its photomechanical 



changes. (Not yet published.) 

 Rochon-Duvigneaxjd, a. 1917 Les fonctions des cones et des batonnets. 



Ann. d'occulistique, Nov., pp. 1-16. 

 Schultze, M. 1866 Zur Anatomic und Physiologic der Retina. Arch. f. 



micros. Anat., Bd. 2, S. 175-286. 

 Tafani, a. 1883 Parcours et terminaison du nerf optique dans la retine des 



crocodiles. Ar. Ital. de Biol., T. 4, pp. 210-233. 



