202 THE FUNDAMENTAL ASPECT OF COLORATION 



females : forty-three control larvae reared in ordinary glazed cages 

 gave 20-9 per cent, green pupge, while forty-six larvae reared under 

 orange-coloured glass produced 93-4 per cent, green pupae. Larvae 

 derived from imagines emerging from these green pupae were, in 

 their turn, submitted to the same orange rays and, on transforming, 

 95-2 per cent, of the pupae were found to be green. The latter were 

 again used for rearing a third generation, but in this case the larvae 

 were reared under similar conditions to the controls. Only 

 thirty-one pupae were obtained, but all were green. The butter- 

 flies from these were segregated into two batches — early-emerged 

 and late-emerged. In the first batch their offspring were allowed 

 to pupate on a varied selection of surfaces, and 58 per cent, of 

 green pupae resulted (from a total of fifty individuals). The 

 offspring of the other batch of butterflies were reared in cages 

 whose glass walls were painted black, and 96-4 per cent., of the 

 forty-eight pupae which resulted, were green. The results are 

 presented as they stand, and Harrison does not attempt any 

 theoretical discussion of the factors involved. 



(/) The phenomena of colour change in the stick insect Carausius 

 have attracted the attention of several recent workers in Germany, 

 notably Atzler (1930), Giersberg (1928) and Priebatsch (1933). 

 This insect is able to change its general coloration in response to 

 sudden changes in its immediate surroundings, becoming darker 

 or paler, as the case may be. Other stimuli, such as temperature 

 and mechanical pressure, elicit a similar response. This response 

 is brought about by movements of the pigment in the hypodermis. 

 The pigment granules either become aggregated or diffused, 

 according to whether the insect becomes paler or darker in its 

 general colour. The primary sensation of the background colour 

 is received by the eyes, which act upon the visual centre in the 

 brain, and apparently induce the secretion of a hormone into the 

 blood. It would appear, therefore, that it is this hormone which 

 activates the movements of the pigment granules. Destruction 

 of the tritocerebrum causes all colour response to cease. Carausius 

 is unique among insects in that its colour response seems to 

 operate in a manner similar to those animals which have true 

 chromatophores controlled by hormone secretion. It would. 



