320 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
boundary of the advancing pigment, a general visual comparison of 
the slides under the microscope afforded a better basis for judgment 
than could be obtained by actual measurements. The values given in 
the columns under BV, G, YG, Y and R (standing for the colors 
blue violet, green, yellow-green, yellow, and red, respectively) were 
estimates, on a scale of ten, of the distance the pigment had migrated, 
regarding the basement-membrane as a starting point and the row of 
nuclei in the distal ends of the retinular cells as the terminus. Thus, 
in series 3 the blue-violet occasioned the pigment to migrate the 
whole distance and was evaluated at 10, while red elicited it for only 
6 tenths the distance. This series, which grades with respect to 
influence on migration from blue-violet through green and yellow 
to red, is photographically reproduced in Plates 2 and 3. In Fig. 3, 
Plate 2, which exhibits the effect of blue-violet, the pigment is out 
around the nuclei of the retinal cells; in Fig. 4, Plate 2, (effect of 
green) it has migrated slightly beyond the boundary (the broken 
line in left half of photograph) of the tapetal layer, but not so far 
as the row of nuclei (indicated by dotted line); in Fig. 5, Plate 2, 
(yellow) the pigment and tapetum are coextensive; but in Fig. 6, 
Plate 3, (red) the pigment, though coextensive with the tapetum at 
the center of the retina, falls short of the outer boundary of the 
tapetum on the sides (as the left half of the photograph has been 
retouched to indicate). All retouching for sake of emphasis, has 
been restricted to the left half of each photograph. 
The summary of results in the lower portion of Table I shiwal 
reading horizontally, that for BV vs. G, out cf 6 trials (a trial being a 
comparison of two animals in the same series), blue-violet showed the 
greatest migration 4 times; for BV vs. YG, blue-violet was more 
effective 3 times, yellow-green once, while twice they tied; for BV 
vs. Y, blue-violet was more effective 2 out of 3 trials; but for G vs. 
Y, each evoked more migration that the other 3 times out of 6. In 
the case of BV vs. R, allowing for the fact that in series 7 and 8 certain 
modifications were made in exposing to red, increasing either the in- 
tensity or the time of exposure in order to obtain a migration equiva- 
lent to that with blue-violet, it is maintained that, including these 
with the other series, the blue-violet outweighed the red in efficiency 
9 out of 10 times. In addition to this there were six preliminary 
series in which red failed to evoke as much migration of the pigment 
as the other colors did. 
The evidence furnished by these observations is conclusive only for 
the difference in efficiency between the extremes of the spectrum. 
