PHOTOMECHANICAL CHANGES IN THE RETINA 539 
However, in the retina of the ape, which has a minute amount of 
pigment composed of needle-shaped granules, the pigment was 
extended 3 to 4 granules deep in the light and only 2 to 3 granules 
deep in the dark. 
In summarizing the foregoing results concerning the effect 
of light upon the retinal pigment, it can be said that the most 
extensive migrations are found in fishes and in anuran amphib- 
ians, whereas the positional changes in the pigment of urodeles 
are relatively limited. Clearly defined movements of the 
retinal pigment also occur in both day- and night-birds. Al- 
though among reptiles and mammals the evidence is conflict- 
ing, it is probable that in some cases slight changes have been 
detected. 
The first observation of the action of light on the cone cell was 
reported by Angelucci (82), who maintained that a shortening 
and thickening of the outer member (ef. figs. 3 and 4, prs. dist. 
con.) was produced by an exposure of the frog’s retina to light. 
This he still supported in later papers (’90), (05), although 
Chiarini (’04 b) has suggested that a passive swelling probably 
occurred and Garten (’07) also failed to corroborate Angelucci’s 
results. 
The positional changes of the inner member of the cone cell 
through the action of ight, was observed in 1884 by Stort, a 
student of Englemann, and the first announcement was pub- 
lished by the latter (85). To the contractile portion of the 
inner member, between the external limiting membrane and the 
ellipsoid, Englemann gave the significant name of myoid (cf. figs. 
3 and 4, my. con.). In some fishes a shortening of the myoid to 
ten per cent of the length which it assumes in darkness occurs 
through the action of light. If effective at all, light causes a 
shortening, and darkness a lengthening in the cone myoids of all 
vertebrates (figs. 3 and 4). 
Stort (87) extended his first discovery on the frog by experi- 
mentation upon representatives of the other vertebrate classes. 
He reported that a similar condition existed in the cones of Perea, 
Triton, Columba, and Sus. His measurements of one dark- 
adapted human eye do not, however, prove that movements of 
the cones occur in man. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 6 
