EFFECT OP LIGHT ON THE RETINA 169 



('81) briefly states (pp. 21 and 35) that there are no rods in the 

 retina of Testudo or of Lacerta, while Cheivitz ('89, p. 143) 

 adds that in Emys europaea and L. viridis there is but one form 

 of visual cell which, from its form, is a cone. 



Krause ('93) finds that in Chelonians there are no rods, and 

 that the elements which had been earlier described as rods were 

 nothing more than cones without oil drops. In L. agilis, how- 

 ever ('76 and '93), he describes rods as being present, but scarce, 

 though in certain places they are found thick together. Anguis 

 fragilis and L. viridis have only cones. 



According to Angelucci, ('94, see Garten, p. 25) Testudo marina 

 has no rods and Greeff ('00, p. 123) makes the brief statement 

 that the reptilian retina (lizards, snakes and tortoises) has onl}^ 

 cones. Chiarini ('06) says that the neuro-epithelium of lizards 

 is formed exclusively of cones of various sizes. Garten ('07, p. 

 24) points out that in Tropidonotus there are no rods, that 

 in Testudo graeca there are probably none, and that in the 

 Chameleon there are certainly no rods. 



Putter ('09, p. 103), concludes from the mode of centripetal 

 connection (dendritic) of the visual cells of the reptiles that all 

 of them must be cones, although the form of the single elements 

 can be very different, e.g., in Anguis fragilis and in the Gecko 

 there are found cylindrical or rod-like outer segments. But he 

 adds that all Chelonians have conical outer segments. 



Hess ('10, p. 281) gives a review of the literature and states, 

 that, in addition to the anatomical features of the retina indi- 

 cating that there are no rods, the futile endeavors of several in- 

 vestigators to obtain evidences of visual purple in the tortoise 

 retina indicates that there can be no rods present. And finally 

 Franz ('13, p. 52) in a very incomplete and, in some particu- 

 lars, incorrect review makes the statement that tortoises possess 

 both rods and cones. 



From these papers the conclusion may be drawn that cones 

 are by far the principal visual element of the retina of tortoises 

 and of lizards. Further that rods may occur in a few, but that 

 they are scarce. It is to be regretted that good figures of the 

 visual cells are not given in anj^ of the articles reviewed. More- 



