166 S. R. DETWILER 



pigment epithelium, in which he regards the migration of the 

 pigment to be bound up with the using up and regeneration of 

 visual red in the rods, he concludes that pigment migration 

 should not take place in a rodless retina, such as the lizards 

 have. Boll, however, cannot say whether it does or not. 



Angelucci ('94) (see Garten, p. 68), however, found that in 

 Testudo marina the pigment does migrate, though less strongly 

 than in the frog. And Chiariili ('06) was also able to clearly 

 demonstrate pigment migration in the retina of the lizard (L. 

 agilis) . He figures, rather diagrammatically, side by side a dark 

 and light retina, and, although he gives no measurements of the 

 extent of the migration, it is clear that the pigment in the illumi- 

 nated eye is nearer the external limiting membrane than it is 

 in the dark eye, covering the paraboloids and drawing away from 

 the bases of the pigment cells so that their nuclei are entirely 

 uncovered. 



Garten ('07, p. 68), however, was unable to obtain prepara- 

 tions of the retina of Emys, Chameleon or of Lacerta which 

 showed constant differences in the position of the pigment accord- 

 ing as to whether the animal had been kept in darkness or in 

 bright light. His results will be referred to again. And finally 

 Hess, ('10, p. 281), was no more successful than Garten with 

 Emys europaea, the position of the pigment in eyes of indi- 

 viduals that had been kept for 22 hours in darkness, 2 hours in 

 sunlight and several hours in light of weaker intensity being in 

 all not markedly different, the outer segments being always 

 covered by a mantle of pigment. 



Concerning the contraction of the cones in light, Engelmann 

 ('85, p. 500) found that in the eye of the snake Tropidonotus 

 natrix, which contains no rods in the retina, the cones contracted 

 but little. Also that in Testudo graeca it is doubtful whether 

 any contraction takes place. Angelucci ('94) (see Garten '07, 

 p. 25) however, claims that in Testudo marina contraction of 

 the cones does take place, though less in extent than in the 

 frog. Chiarini ('06) also reports that in the eye of L. agilis the 

 cones shorten when the eye is brightly illuminated, but only 

 slightly, for the cones measure in dark eyes 25-35;u, in light eyes 



