546 LESLIE B. AREY 
by Garten (’07), who suggested the possibility that the basal part 
of the pigment cell (figs. 1 and 2, pd. cl. pig.) is concerned in all 
activities heretofore ascribed to the pigment, whereas the move- 
ment of the pigment in the processes has an entirely different 
significance. 
The expansion of pigment in the retina of the frog was con- 
sidered by Herzog (’05) to be of use in storing up radiant energy, 
in the sense that the dark heat waves thus made available would 
accelerate the chemical processes taking place in the photo- 
receptors. 
Chiarini (’06) believed that the function of the migrated 
pigment is nutritive, the rods and cones thereby being recom- 
pensed for the losses which they incur during functional activity. 
The pigment was also supposed to protect the visual cells from 
overstimulation by light. 
It has been suggested that the expanded pigment surrounding 
the outer members of the visual cells serves to absorb all light 
which escapes from the rods by refraction and thereby makes 
possible an independent stimulation of the individual cells. 
Garten (’07) investigated this experimentally and showed that 
light, entering the rods of mammals (these elements not being 
surrounded by pigment), underwent total reflection, while in 
lower vertebrates the refraction was such that light did escape 
from the outer members of the rods and was presumably kept 
from entering adjacent rods by being absorbed in the expanded 
pigment. 
These latter results are very suggestive since the conclusion 
drawn by Garten possesses the merit of having been based upon 
actual observation. It would be interesting to ascertain whether 
this correlation between pigment migration and the refractive 
index of the rod’s outer member extends throughout all classes 
of vertebrates. Garten’s data were obtained from several mam- 
mals and fishes, and from the frog; the crucial test, however, 
would consist in determining the indices of refraction of the rods 
in the pigment-free retinas of certain elasmobranchs, in the retinas 
of urodele amphibians, where both the amount of pigment 
