214 LESLIE B. AREY 



some workers that tliis interrelation is independent of the brain, 

 but also tliat it continues after the optic nerve is cut distal to 

 the chiasjua. The latter assertion, however, has been the sub- 

 ject of much controversy. 



Observations on the frog relative to these conditions have 

 • been presented by the following workers: Englemann ('85), Grijns 

 ('91) ; Nahmmacher ('93) ; Angelucci ('90; '05); Lodato e Pirrone 

 ('01); Chiarini ('04) and Herzog ('05). Similar statements were 

 made by Pergens ('96) for fishes, and by Birch-Hirschfeld ('06) 

 for the pigeon. The diversity of stimuli which have been reported 

 as being effective in producing positional^ changes in the cones 

 and pigment has caused Pick ('89; '90; '91) to doubt the reflex 

 nature of the process, although some of his own experiments by 

 no means disprove many of the contentions of the other investi- 

 gators. More recently Fujita ('11) has shown wherein the older 

 experimentation on the interdependence in the responses of the 

 elements of the two eyes through the action of light, is not 

 trustworthy. 



Englemann ('85), who was the pioneer in asserting the pres- 

 ence of 'retino-motor' nerve fibers, further supported his view 

 with results obtained by illuminating the skin only of dark- 

 adapted frogs, whence changes in the cone cells and retinal pig- 

 ment were said to occur. This observation, however, is not in 

 agreement with those of Fujita ('11) and myself (Arey, '16). 



A number of other statements are on record which ascribe a 

 control over the movements of these elements to the central 

 nervous system. An enumeration of stimulating agents supposed 

 to act in this way would include such as the following: noises, 

 unilateral pressure on the eyeball, mechanical irritation (Ange- 

 lucci, '90), and trussing up a frog for 24 hours (Herzog, '05). 



The first direct experimentation in which the relation of the 

 optic nerve to movements of the retinal elements was tested 



elongation taking place when the retina is again subjected to darkness (figs. 10 

 and 11). In fishes and birds, at least, the rod myoid is likewise contractile (figs. 

 10 and 11), although the direction of movement in light and in darkness is the 

 exact reverse of that executed by the cones. For a review of the literature on 

 this question, reference may be made to an earlier paper by the writer (Arey, 

 '15). 



