324 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
successive days on account of deterioration manifested in the eye by a 
gradual diminution in the migration, so that usually only one, or 
sometimes two, legitimate matchings in amounts of migration evoked 
by the two colors could be obtained for each animal. 
In order that the results might be compared and summarized in 
some way, it was necessary to assign a quantitative valuc to the 
amount of migration exhibited by each recorded sketch after com- 
paring it with an arbitrary standard. This standard was a circle, 
made with the same stamp as those in the records, with a dark area 
in the center representing a medium amount of migration which, 
based on a scale of 5, was evaluated at 3. Each migration-record, 
therefore, was referred to this standard, judged for its relative amount 
of migration, and assigned a value accordingly. Table II contains 
these evaluations in the vertical columns under the distances at 
which the exposures were made (50, 100, etc. cm.). In the right hand 
portion of the table are given those distances — deduced from the 
assigned values either directly, where one in red équalled one in blue- 
violet, or indirectly by interpolation — at which red is probably 
equivalent to blue-violet in eliciting the migration. Discretion had 
to be ex.rcised in determining the validity of evaluations chesen for 
comparison, because, owing to deterioration in the rcsponse of the 
pigment accerding to the sequence of the exposures, certain cases 
apparently equal in the table were quite incomparable. Taking 
animals K and L for example, the exposures for both were in the fol- 
lowing sequence:— to BV at 400 cm. (Jan. 24), 300 em. (Jan. 26), 
200 cm. (Jan. 27); to R at 150 cm. (Jan. 30), 100 cm. (Jan. 31), 
50 em. (Feb. 1), the progress through each color being from the lower 
to the higher intensity. Although two days of rest were allowed 
between the last exposure to blue-violet and the first to red, yet the 
exposure on the third consecutive day to red showed evidence, if 
one compares the values for 50 cm. with those at 100 cm., of exhaustion 
in the eye. Again, in animal 38, where red was tested at 50 cm. at 
the beginning and again at the end of the series, this deterioration was 
manifested. Final deductions from the assigned evaluations were 
made, therefore, after the sequence of exposures had been taken into 
consideration. The distances at which the efficiencies of the two col- 
ors were on a par were averaged and equated, thus R at 107.5 cm. = 
BV at 247 cm. Since the latter distance was 2.29 times the former, 
the intensity of the former wus (2.29)? times the latter, 7. e. BV = 
5.2 R in terms of power to elicit the migration of pigment. 
In order to verify the results obtained by this necessarily artificial 
