326 bulletin: museum of comparative zoology. 



and devious method of comparison, a new and independent set of 

 evaluations was made, given in Table III, for the same migration- 

 records i. e. for those used in Table II. This time the standard of 

 reference consisted of a graded series of migrations exhibited by 

 animal 28 in three separate exposures to red at a distance of 150, 

 100 and 50 cm. This series was evaluated at 1.5, 3, and 4, respectively, 

 and was used as a scale by which to judge the other records. Not only 

 was the value of sequence weighed again, but the records of animals 

 of dubious physiological status were marked and, in the averaging, 

 were taken into consideration. When all the animals were averaged, 

 the final equation was BV = 6.5 R; after rejecting animals G, K, 24, 

 25, 35, and 36, this became lowered to BV = 5.6 R. Returning to 

 Table II, the elimination of the same animals raised the final result 

 from 5.2 to 5.6, showing perhaps that these animals were so dubious 

 as to make the results oscillate up and down. From Tables II and 

 III the final expression, therefore, for the elicitibility of pigment- 

 migration, determined by varj'ing the intensity, was reduced to BV = 

 5.6 R approximately. 



(2) Time of exposure varied. In this modification of the experi- 

 ment, instead of making several exposure tests with both colors, 

 only one exposure was made with blue- violet (for a five minute 

 period), while three were made with red viz. for 20-, 30-, and 45- 

 minute periods, with the expectation of securing amounts of mi- 

 gration less than, equal to, and greater than that evoked by the 

 blue-violet. 



Throughout this series of experiments the crayfish were usually 

 exposed only every other day, in order to minimize the disturbing 

 factor of deterioration. Table IV was compiled in a manner similar 

 to that for Table II by evaluating with reference to a single arbitrary 

 standard condition, while Table V was based, similarly to Table III, 

 upon an independent set of values assigned relative to tlu-ee graded 

 and evaluated migrations from the records of animal 22. The 

 average of each column of values under the respective exposure- 

 periods was taken. Since the average evaluation for red at 30 

 minutes was smaller, while at 45 minutes it was greater, than that 

 for blue-violet at 5 minutes, by interpolation the period of time at 

 which red would have equalled the effect of blue-violet at 5 minutes 

 was computed to be 36.8 minutes in Table IV, and 39 minutes in 

 Table V, or, if averaged and reduced to the previous equation, 

 BV = 7.6 R. Another determination, made from Table V by inter- 

 polating for the requisite periods of time in each individual set of 



