ECOLOGY AND BOTANY^ MICEOSCOPY, ETC. 201 



The second kind of colours belongs to the hypodermis — hypo- 

 dermal colours — and are the consequence of a chemical process, 

 generating colour out of substances contained in the body of the 

 insect. These colours may be changed into other colours by light 

 and heat, perhaps by acids or by the influences of the sexual organs. 

 If such a change were to a certain extent a photographic process, 

 some important facts (mimicry) could be understood, which otherwise 

 are inexplicable. The hypodermal colours are generally brighter 

 and lighter than the dermal, and mostly fade, change, and disappear 

 after death, an exception existing, however, in the case of certain 

 colours of the elytra and wings, of the hairs, scales, and appendages 

 of the body. The hypodermal colours are very often different in 

 males and females of the same species, but the dermal more rarely 

 differ. The former change during life-time by sexual influences, 

 cold, &c. 



There occur in a number of insects external colours, that is, 

 colours upon the cuticula, which are displaced hypodermal colours : 

 produced in the hypodermis and exuded through the pore canals 

 — the nearly pale blue or white upon the abdomen of some Odonata, 

 the white on many Hemiptera, the pale grey on the elytra and on the 

 thorax of the Goliath beetle, and the yellowish powder on Lixus. 



The question of the pattern is then considered, the author 

 believing that a more detailed study of the different patterns which 

 are to be found in different groups, and perhaps the development of 

 the law according to which the pattern is changed in different groups, 

 would advance us nearer to the knowledge of its nature and origin. 



The pattern is not the product of an accidental circumstance, but 

 apparently the consequence of certain events or actions in the interior 

 of the insect mostly at the time of its development. The proof is 

 easily afforded by the regularity of the pattern in the same genus or 

 the same family. If studied carefully and comparatively, the pattern 

 for such a genus is the same for all species, but for some of them 

 more or less elaborated. 



Weismann, in his study of the origin of the pattern of caterpillars 

 of the SphingidsB, contends that all the patterns and colours possess 

 only a biological value. The green colour, which first appears, 

 corresponds to that of the leaves. But in a large caterpillar one 

 main colour would be too apparent ; therefore longitudinal lines 

 separate the main colour into several fields and diminish the danger, 

 the more so when the caterpillar lives among grasses. The oblique 

 lines form a similar protection, and are even more effectual when the 

 lines have coloured borders, which make them resemble the ribs of 

 leaves. The eye-spots of GJicerocampa are said to frighten enemies, 

 and the variegated colours of DeilepMla to designate them as not 

 eatable. The dark colour of full-grown caterpillars of Chcerocam^pa 

 is said to be owing to the impossibility of being protected by any 

 colour, on account of its large size. These caterpillars acquire, there- 

 fore, the habit of feeding at night, and hide themselves during day- 

 time under dead leaves. As, therefore, every one of the characters 

 is of biological value, they can be explained by means of natural 



