142 LESLIE B. AREY 



not fairly test the effect of this temperature on pigment migration. 

 One could hardly expect the body temperature of the animals 

 to become adjusted to that of the apparatus in such a short time, 

 especially since the heating was progressive and the final tem- 

 perature was not realized until the end of the experiment. 



At 32°C. the pigment had extended to the maximal distance 

 but the distribution was nearly homogeneous. 



A condition of extreme expansion occurred at 37°C. A dense 

 massing of pigment near the external limiting membrane masked 

 the rod ellipsoids completely, while the outer members of the 

 rods were nearly free from pigment. When the temperature 

 was raised to 39° or 40°C. clonic spasms occurred which ended 

 in death; the pigment, nevertheless, retained the same position 

 as at 37°C. 



A second series of experiments, in which frogs were cooled 

 in a refrigerating apparatus, showed that a subjection to 0°C. 

 in the dark for 2 hours produced incomplete expansion, while 

 after 3 hours the pigment was distributed in a zone of maxim_um 

 breadth, but with only a slight tendency toward distal massing. 

 This discovery, which was Herzog's most interesting contribu- 

 tion, is not only in disagreement with the commonly quoted 

 result of Ewald und Kiihne's earlier work, but also has not been 

 substantiated by the recent investigation of Fujita ('11), who, 

 however, states that high temperature does induce pigment 

 expansion, as the'other investigators have all maintained. Fujita 

 tried the effect of ^ow temperature on only four animals, the 

 duration of his experiments ranging from 30 minutes to 6 hours, 

 yet he drew the following positive conclusion (p. 170) : "Das 

 Resultat war in alien Fallen das gleiche: ich konnte keine Hell- 

 stellung konstatieren. Die Zapfen waren nicht kontrahiert, das 

 Pigment nicht vorgewandert." 



Since all these results on the frog's retinal pigment are not 

 only fundamentally different from those found by me in fishes, 

 but also have no parallel in the movements of vertebrate and 

 invertebrate melanophores, and since, moreover, there is no 

 general agreement concerning the effect of low temperature, a 

 thorough reinvestigation of the problem seemed to be needed. 



