256 THE entomologist's record. 



portant part in the general appearance of such insects than thoy do in 

 our duller climate ; still, I should expect it would be a part only (in the 

 Lepidoptera) and that we should find alnindant pigment-factor granules 

 too. The test as to whether interference is the cause of colour is the 

 variability of the colour at vai-ying angles of the incident light ; but 

 as I endeavoured to show in the case of T. quercns, interference alone 

 does not explain the j)urple gloss, but, plus pigment, it helps to do so. 



" Why are many nocturnal insects highly coloured ? Can they 

 admire one another in the dark?" Mr. Burrows asks. Is not colour, in 

 the large majority of insects, for protective and not attractive purposes ? 

 Does it not rather correspond with the seasons and with the environ- 

 ment ? Then again, we may rememljer that many insects have two 

 flights — one, in the very early morning when light abounds. 



As to tlie fading of colours on exposure. Is not this comparatively 

 easy to understand, if we consider that it is the absorbing and reflecting 

 pigment-factor that is really affected ? Some of the sun's rays split 

 into two the carbonic acid (CO2) absorbed Ijy the chlorophyll cells of the 

 green leaf, fixing the one constituent, and liberating the other. Some 

 of the sun's rays split up the nitrate of silver of our photographic films. 

 Is it not reasonable therefore to suppose that some of its rays may so 

 gradually alter a pigment-factor, that it may lose in varying degrees 

 its jDrevious relative power of reflection and absorption ? This would 

 apply equally to the absorption-factor of black, though, as I have re- 

 marked before, I think even the purest blacks (in Lepidoptera) are only 

 relative, and are, in reality, coloured. — W. S. Riding, M.D., Buckerell, 

 E. Devon. April 2nd, 189o. 



I quite agree with Dr. Riding that the colours of insects are for 

 protective purposes. I have never lieen able to understand Darwin's 

 position witli regard to the supposition that insects selected their mates, 

 or that sexual selection to this extent was possible, even in day-flying 

 insects. In Secondary Sexual Characters, p. xviii., I have discussed this 

 at length, and pointed out the advantage of Wallace's argument over 

 that of ]Jar\vin in explanation of sexual dimorphism, illustrating my 

 remarks by reference to the genus Lycaena. The observations I have 

 made lead me distinctly to believe that there is iDractically no reason 

 for considering that insects have developed any colours for attractive 

 purjDoses. There can be no doubt that moisture covers thinly, as it 

 were, the scales of some insects when tliey first emerge from pupa?. The 

 whole surface of the insect is distinctly moist on its emergence, and 

 there is no doubt that this film of moisture Avould produce interference 

 results. The fact that these interference colours persist in some butterflies, 

 such as the Meadow-browns, for two or three days, would suggest that 

 the moisture is coagulable, and that it retains its power until a con- 

 siderable period of flight has worn it off. I only suggest this as an 

 additional reason for the presence of these colours in special cases ; the 

 cxi^lanations already given by Dr. Riding, are reasonable enough. — 

 J. W. TuTT. May 7th, 1895. 



The frenuluji: of the British species of Smerinthus. — Mr. 

 Bacot, in his interesting paper on the genus Smerinthus (ante, p. 178), 

 refers to that singular Heterocerous structure, the frenulum, as developed 

 in the three British species of that genus. As I have studied this 

 organ for several years past, and in the course of my study have 

 examined many hundreds of species of British and Exotic "^moths, 



