524 WM. A. KEPNER AND A. M. FOSHEE 



The functional changes of \dsual cells in certain vertebrates 

 have recently been well described and the literature of the sub- 

 ject reviewed by Detwiler ('16) and Arey ('16). 



Englemann (85, p. 500) found that in the eye of the snake Tropid- 

 onotiis matrix, which contains no rods in the retina, the cones contract- 

 ed but little; also that in Testudo graeca it is doubtful whether any 

 contraction takes place. Angelucci ('94) however, claims "that in 

 Testudo marina contraction of the cones does take place, though less 

 in extent than in the frog. . . ." Chiarni ('06) also reports that in 

 the eye of L. agilis the cones shorten when the eye is brightly illumi- 

 nated, but only slightly, for the cones measure in dark eyes 25 to 35;u, 

 in light eyes 23 to 30/x. Finally Garten ('07) found also a very slight 

 contraction (not more than 1.2^) in the eye of Chamelion. (Detwiler 

 (16) p. 166-7.) 



In speaking of his own work, Det^\dler says : 



Light causes a migration of the pigment and a contraction of the 

 cones in both the tortoise and lizard retina, the extent of migration 

 in the tortoise averaging 3.6/i, and in the lizard 3.1/i. The extent of 

 the" contraction of the cones in the tortoise averages 2.3ju (p. 186). 

 "To the contractile portion of the cone's inner member Englemann 

 applied the significant term 'myoid'. . . . The contractility of 

 the myoid is extraordinary, since in some fishes light produces a short- 

 ening of this part to 10% of the length which it assumes in darkness. 

 If effective at all, light always causes a shortening and darkness an 

 elongation of the cone cell" while the "myoid of the rod-visual cell 

 elongates in light and shortens in darkness" in all investigated verte- 

 brates. 



Arey ('16-b), p. 441. The latest observations, therefore, 

 indicate that a shortening or an elongation of the retinulae 

 takes place by means of a modification of the myoid. The 

 change in the size and shape of the rhabdome has nothing to do 

 with the total length of the visual cell. No change in the ellip- 

 soid of the visual cell of the vertebrate has been recorded. 



The functional changes to light as judged from our study of 

 the fixed condition in the eye of Prorhynchus, stand in sharp 

 contrast to the changes in the retinulae of vertebrates. The 

 reaction of the visual cells to light and darkness is more pro- 

 nounced than that of the pigment cells of the eyes. 



No nuclear change has been observed in the retinula of Prorhyn- 

 chus by us. The change in the cytoplasmic segment, that is 



