v COLOURS OF ANIMALS 847 



Many other cases are known among insects in which the 

 same species acquires a different tint according to its sur- 

 roundings; this being particularly marked in some South 

 African locusts, which correspond with the colour of the soil 

 wherever they are found. There are also many caterpillars 

 which feed on two or more plants, and which vary in colour 

 accordingly. A number of such changes are quoted by Mr. 

 E. Meldola, in a paper on " Variable Protective Colouring in 

 Insects" (Proceedings of the Zoological Society of London, 1873, 

 p. 153); and in some cases it has been shown that green 

 chlorophyll remains unchanged in the tissues of leaf -eating 

 insects, and being discernible through the transparent 

 integument, produces the same colour as that of the food 

 plant. 



In all these insects, as well as in the great majority of 

 cases in which a change of colour occurs in other animals, the 

 action is quite involuntary; but among some few of the 

 higher animals the colour of the integument can be modified 

 at the will of the individual, or at all events by a reflex 

 action dependent on sensation. The most remarkable case of 

 this kind occurs with the chameleon, which has the power of 

 changing its colour from dull white to a variety of tints. 

 This singular power has been traced to two layers of movable 

 pigment-cells deeply seated in the skin, but capable of being 

 brought near to the surface. The pigment-layers are bluish 

 and yellowish, and by their contraction or concentration these 

 can be forced upwards either together or separately. When 

 the animal is passive the colour is dirty white, which changes 

 to various tints of bluish, green, yellow, or brown, as more or 

 less of either pigment is forced up and rendered visible. 

 The animal is excessively sluggish and defenceless, and its 

 power of changing its colour so as to harmonise with sur- 

 rounding objects is essential to its safety. Here too, as with 

 the pupa of Papilio Nireus, colours such as scarlet or blue, 

 which do not occur in the natural environment of the animal, 

 cannot be produced. Somewhat similar changes of colour 

 occur in some prawns and flat-fish, according to the colour 

 of the bottom on which they rest. This is very striking 

 in the chameleon shrimp (Mysis chamseleon), which is 

 gray when on sand, but brown or green when among sea- 



