66 



VERTEBRATE PHOTORECEPTORS 



complete absence of cones (Figure 47). The rods resembled 

 in many respects those of the rat, but were found to be 

 slightly longer (v. Table 1). There is no evidence of any 

 fundus specialization such as a macula or an ^area centralis 

 retinae' as Woollard (1925) described for the eye of the 

 nocturnal Tarsius spectrum. The presence of an area cen- 

 tralis retinae in the eye of Tarsius and its supposed evolu- 

 tionary relationship to the fovea, as advanced by Elliott- 

 Smith (1928) will be discussed later. Both Galago and Nyc- 

 ticebus showed the complete absence of epithelial pigment 





Fig. 47. a, retina of Galago mala near the ora serrata. X 420. b, retina of 

 Nycticebus tardigradus from fundus showing rods and absence of epithelial 

 pigment. X 300. c, same as b. X 420. (From Detwiler, 1940, Anat. Rec, 

 V. 76.) 



in the fundus, and only as the ora serrata is approached does 

 one see pigment (Figure 47, a). Both forms possess a fibrous 

 tapetum lucidum (choroidal tapetum) (Figure 7). 



From Woollard's description of the eye of Tarsius one is 

 led to believe that the epithelial pigment layer contains 

 abundant pigment for he says, ''The characters of this more 

 anterior part of the retina agree very well with the structure 

 of the retina found in animals of nocturnal habits. This is 

 shown in the large amount of pigment and in the outer 

 layer of the retina." One is left in doubt as to the extent of 

 epithelial pigment in the fundus of the retina. Extensive 



