THE EFFECT OF LIGHT ON THE RETINA OF THE 

 TORTOISE AND THE LIZARD 



S. R. DETWILER 



From the Osborn Zoological Laboratory, Yale University 



ELEVEN FIGURES 



INTRODUCTION 



Since the discovery of the migration of pigment by Boll ('77) 

 and by Kiihne ('77) and of the contraction of the cones by van 

 Genderen Stort ('87,) (see Engelmann, '85) in the retina of the 

 frog, this subject has been carefully investigated by many authors 

 in many animals. Garten ('07) has brought together the main 

 and important results of this work on the changes induced in 

 the retina by light. From this we see that light produces a 

 variety of effects on the form and staining reactions of the 

 different parts of the retina. Of these effects three are particu- 

 larly interesting to us. 1) Migration of the pigment in the epi- 

 thelial cells of the retina. 2) Changes in form and position of 

 the visual cells. 3) Changes in form, position and ability to 

 stain of the ganglion cells and of the nuclei of the inner and outer 

 granular layers. 



As far as the reptiles are concerned these question^ seem far 

 from settled, and therefore worthy of further investigation. In 

 the first place concerning the migration of pigment, Angelucci 

 ('78, p. 372) was not able to say from the results of a few experi- 

 ments on the turtle, Testudo graeca, and on lizards (L. agilis, 

 L. muralis and L. viridis), which have no rods, whether pigment 

 migration took place or not. If it does, he remarks, it is much 

 less marked than in the amphibian eye. Boll ('81, pp. 20 and 

 21) in an incompleted work, also considered this matter and in 

 a theoretical consideration of the physiological properties of the 



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