354 S. R. DETWILER AND HENRY LAURENS 



A refractive disc is demonstrable in the inner segment of a 

 large number of the cones, its occurrence having no correlation 

 with the presence or absence of a paraboloid. It is clearly shown 

 in types c, d, and e with paraboloids, and types / and h without 

 paraboloids. Cones without both paraboloids and refractive 

 discs (type g) are rare, and their presence is most common in the 

 region near the entrance of the optic nerve. 



A search for double cones has been without success. In a 

 number of regions, types h and g could be found in rather close 

 relationship, simulating a double cone, but the loose intunacy of 

 the two elements could hardly warrant their being called double. 

 The absence of well defined double cones is in striking contrast 

 with their common occurrence in the retinae of reptiles in gen- 

 eral (see Detwdler '16, Laurens and Detwiler '20), but in agree- 

 ment with conditions in the retina of Chameleon (see Garten '07 

 and Rochon-Duvigneaud '17), which contains single cones only. 



As the fovea is approached the cones gradually become more 

 and more slender and cylindrical in form, accompanied by a 

 loss of the paraboloid bodies and oil-drops. At the apex the 

 visual elements, as above mentioned, are so small and attenuated 

 that their structure cannot be definitely determined by the use 

 of the highest microscopic magnification at our command. 

 Their general shape, in so far as could be determined, is show^n in 

 figure 4 and bears a close resemblance to the foveal elements 

 of the human eye (see Schultze '66, fig. 3, PI. 13). . 



Pecten. The pecten is a conical shaped structure approxi- 

 mately 1 mm. in length, with its base applied to the inner surface 

 of the optic nerve at its entrance, and its apex projecting dor- 

 sally into the posterior chamber of the eye (figs. 1 and 2). It is 

 very vascular; thus indicating its function as a nutritive organ. 

 It is also deeply pigmented — the pigment occurring in the form 

 of minute granules which are scattered throughout the stroma 

 of the organ. In general, in shape and structure, it resembles the 

 pecten found in the eye of Sceloporus (Detwiler '16). 



The presence of a pecten has been demonstrated in a number 

 of reptilian eyes. Heinemann ('77) found a small pecten in the 

 eyes of several Chelonians. Its presence in. the eyes of a number 



