. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 692 Comparative Animal Physiology lowish and black pigments the locusts may become yellowish-white, brown, or black. The quantity of black pigment formed seems to depend on the ratio of incident to reflected light striking the eyes; the amount of the yel- lowish pigment appears to depend on the predominant wave lengths of the light present, being formed more rapidly at longer wave lengths (550-660 m/i) and less rapidly at shorter ones (450-500 m/x). When this species enters its swarming, migratory phase a skin c
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 692 Comparative Animal Physiology lowish and black pigments the locusts may become yellowish-white, brown, or black. The quantity of black pigment formed seems to depend on the ratio of incident to reflected light striking the eyes; the amount of the yel- lowish pigment appears to depend on the predominant wave lengths of the light present, being formed more rapidly at longer wave lengths (550-660 m/i) and less rapidly at shorter ones (450-500 m/x). When this species enters its swarming, migratory phase a skin coloration darker than in the solitary phase is produced. There is some evidence that the darker coloration is a result of the more intense metabolic activity. When migrating locusts are returned to solitary conditions they will regain their lighter color phase, but this color change is delayed if the isolated locust is kept in a constantly ex- cited state.'*'' A few insects show color change which can be traced to redistribution of pigments within pigment cells or chromatophores. Corethra shows a rapid physiological color change of its air sacs.'"'* This last is due to the presence of special pigment cells. On a black background the pigment becomes dis- persed and the pigment cells are scattered uniformly over the sacs. On a. Fig. 261. Diagram illustrating the use of a moist chamber as a stimulus for producing darkening in Dixippus. The darkening in this instance is in response to abdominal stimu- lation and commences at the head and passes posteriorly only as far as an anterior thoracic ligature. From ;* white background the pigment concentrates and the cells appear to wander to one side of the sacs. The eyes are involved in these reactions, as is also the brain. The color changes of the Phasmid, Dixippus morosus, have been investi- gated rather extensively. The hypodermal cells of this species contain four pigments, brown (melanin), orange-red and yellow (
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