14 



have all the features of the pale-coloured group first mentioned 

 above, and indeed has the closest resemblance to some of its 

 members. Close attention shows it to have a very slight metallic 

 lustre, and a still more minute examination reveals two other 

 rather recondite characters, namely, the toothing of the front tibiae 

 and the middle claws of the female, by which its true affinities 

 are shown to be quite different from its apparent ones. 



It is thus evident that, greatly as the coloration of these 

 insects is liable to vary, this variation has definite limits, and in 

 order that we may not be bewildered by it, it is important to 

 ascertain as far as possible the principles by which it is governed. 



As horticulturists find that within a certain range of colours 

 variations are easily produced, whilst others are practically incom- 

 patible, it is no doubt the case with insects that colour- variation, 

 although sometimes appearing almost unrestrained, is actually 

 limited to shades which are distinguished by a minimum o'f 

 chemical difference, minute chemical changes sufficient to produce 

 these occurring at a sensitive period in the development, possibly 

 under the influence of environmental conditions. A certain range 

 of metallic colours, of which brilliant greens are the predominant 

 tints, seem the most liable to variation of this kind, and typical 

 instances are Anomala, fulviventris and A. polymorpha, of which, 

 although very brilliant, it is quite impossible to say what is the 

 normal colouring. 



Differences of pattern belong to another category, and are 

 dependent on the quantity of pigmented surface, and therefore 

 upon the amount of pigment produced. Pigmentation appears to 

 begin at certain fixed points and to extend in particular directions, 

 forming patterns which are generally very simple and are often 

 found to recur independently in quite unrelated groups some- 

 times forming the basis of mimetic resemblances, in which the 

 shape of the mimic and not the coloration is the more recently 

 acquired character. 



A reduction in the amount of pigment produced may result in 

 the simplification of the pattern by reversion to a more primitive 

 one, or its complication by the failure of small pigment-masses to 

 unite into large ones. 



Generally speaking, pigmentation is slight when the chitinous 

 integument is thin and increases with the strengthening of the 

 latter; soft-bodied insects being very frequently yellowish in 

 colour, while the highest degree of chitinisation is as frequently 

 accompanied by black or very dark colouring. Similarly the 

 darkest-coloured parts of an individual insect are commonly found 

 to coincide with the hardest parts of the external skeleton. Thus 

 in an insect's wing the colouring-matter is generally distributed 

 very thinly through the membrane, but concentrated in the veins. 

 In the body we commonly find a similar concentration at the 

 extremity of leg- and antennal joints, in the jaws, spines, and 

 other highly chitinised parts, the thickened bosses or calli pro- 

 duced near the shoulders and apices of the elytra, and on the 



