CHAP. XIV SPECIFIC HEAT AND INSECT COLORATION 275 



laid her eggs on a stalk, gradually walking up it as she did so. 

 The eggs at the same height on the stem are thus of about the 

 same age ; the lowest eggs are hatched first, and the insects 

 there are accordingly adult while those above are still 

 immature. This does not account for the occurrence of the 

 larvae at the base, which is inexplicable to me, unless they 

 belong to another generation. 



This assumes that the green bud-like and the pink flower- 

 like forms belong to the same species, Mr. Gahan has kindly 

 sorted the specimens into male and female, and found that the 

 colour difference is not sexual. Thus on the Frontispiece^ Fig. 

 2b shows the male, and Figs. 2a and 3 the female form ; these 

 may be distinguished by the greater length of the transverse 

 mark on the hinder margin of the fore -wings of the male. 

 The same difference occurs between the sexes of the green 

 form. 



In every respect, except colour, the two forms are identical, 

 and it therefore seems most probable that they are dimorphic 

 forms of one species, which is Plata nigrocincta (Walker). 



Another point which interested me in reference to insect 

 coloration was the influence of the different capacities for the 

 absorption of heat possessed by different colours. A black object 

 becomes more heated than a white one, when both are exposed 

 under the same conditions. An insect has so much surface in 

 proportion to its bulk, that dark-coloured species are heavily 

 handicapped when exposed to the intense sun of the tropics. 

 This is the simple explanation of the fact, which impressed 

 itself upon me as soon as I began to collect butterflies — that 

 the light -coloured species fly in the daytime, and the dark 

 ones in early morning and at dusk. I made considerable 

 collections at Ngatana, at all hours of the day, to test this point. 

 Thus on 30th January, I began collecting at 5.45 A.M., and 

 found only species which are mainly of dark brown colour, 

 such as Hypoliinnas misippus, Linn., and Jimonia clelia, Cram. 

 At 6.30 a reddish brown species {Lininas klugi, Butl.) began to 

 appear, and this was the only species caught during the next 

 half-hour, though this was abundant. A little before half-past 

 seven a light brown species, Acroia ccecilia, Fabr., made their 

 appearance, followed immediately by numbers of light-coloured 

 butterflies, such as Teracolus syrtinus, Butl., which is all white 



