308 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
for any of the colors, Pergens found that the cones still responded, 
thus confirming Engelmann (’84) in the belief that pigment-migration 
and contraction of cones were independent of each cther for low 
intensities of light. 
The only other investigation of the photokinetic phenomena in the 
vertebrate eye under colored light is that of Herzog (:05). The aim 
of his research was not so much to ascertain the qualitative effects as 
the quantitative, viz., the effects evoked by different intensities of 
the same color. Colored solutions were used as light-filters. The 
intensity of any given color could be varied by changing the voltage 
of the white light by means of a rheostat; but the intensities of 
different colors were compared by judging the distinctness of an object 
as seen through the filters. The contraction of cones was the major, 
the migration of pigment the minor object of investigation. He 
reached the conclusion that the contraction of cones was a function 
of the intensity and also of the wave-length of light; and inciden- 
tally he found that blue was most and red least effective in eliciting 
the migration of pigment. 
The literature on invertebrates begins with Kiesel’s (’94) contribu- 
tion on Plusia gamma. This investigator was the first in studying 
the influence of colored light upon the photomechanical changes in 
the visual organ to make use of the long-known phenomenon of glow 
in the dark-adapted eyes of arthropods. His observations on the effect 
of spectral light are summed up in one rather remarkable statement, 
“Nach meinen Zahlreichen, allerdings mit unzulanglichen Mitteln 
angestellten Versuchen scheint es, als ob ausser den uns sichtbaren 
Strahlen auch Ultraroth, das wir bekanntlich nicht sehen, eine Pig- 
mentverschiebung bei Plusia gamma verursache, dass also auch 
ultrarothe Strahlen von diesem Thiere wahrgenommen werden.” 
The observations of Bell (:06) on the crayfish have been mentioned. 
The most recent work on the problem is that of v. Frisch (:08) per- 
formed on moths and butterflies. Taking advantage of the phenome- 
non of glow, he made a series of tests with extirpated, dark-adapted 
eyes, placing them by couples in different regions of a band of spectral 
light and timing them for the extinction of the glow. This occurred 
first in the violet, next in the blue, but no difference could be detected 
for the rest of the spectrum in the time required for this change. 
From the work of Boll in 1877 to that of Bell in 1906 these researches 
into the problem of photomechanical changes induced in the eye by 
colored light have been carried on (and here the work of Pergens, ’99, 
can not be excepted) with the same, persistent error of method: the 
) 
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