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Show 3G2 SEXUAL SELECTION. PART !II. vermilion metallic tints; and the sexes often differ~ Thus the males of some of the Agrionidro, as Prof. Westwood remarks,(8 "are of a rich Llue with black "wings, whilst the females are fine green with colourless "wings." But in Agrion Ramburii these colours ~re exactly reversed in the two sexes.49 In the extensive N. American genus of Hetrerina, the males al~ne have a beautiful carmine spot at the base of each wmg. In Anax junius the basal part of the abdomen in the male is a vivid ultra-marine blue, and in the female grassgreen. In the allied genus Gomphus, on t~e other band and in some other genera, the sexes d1ffer but little' in colour. Throughout the animal kingdom, similar cases of the sexes of closely-allied forms either differing greatly, or very little, or not at ~11, are. of frequent occurrence. Although with many L1belluhdre there is so wide a difference in colour between the sexes, it is often difficult to say which is the most brilliant; and the ordinary coloration of the two sexes is exactly reversed, as we have just seen, in one species of Agrion. It is not probable that their colours in any case have been gained as a protection. As Mr. MacLachlan, who has closely attended to this family, writes to me, dragonflies- the tyrants of the insect-world-are the least liable of any insect to be attacked by birds or othe.r· enemies. He believes that their bright colours serve· as a sexual attraction. It deserves notice, as bearing on this subject, that certain dragon-flies appear to be attracted by particular colours: Mr. Patterson observed 50 ' that the species of AO'rionidre, of which the males are blue settled in numb 0 ers on the blue float of a fishing ' 4S 'Modern Class.' vol. ii. p. 37. 49 Walsh, ibid. p. 381. I am indebted to this naturalist for the· followin<Y facts on Hetrerina, Ana.x, and Gomphus. so ''r1~a.nsact. Ent. Soc.' vol. i. 1836, p. lxxxi. CnAP. X. NEUROPTERA. 363. line; whilst two other species were attracted by shining white colours. It is an interesting fact, first observed by Schelver,. that the males, in several genera belonging to two subfamilies, when they first emerge from the pupal state are coloured exactly like the females; but that their bodies in a short time assume a conspicuous milky-blue tint, owing to the exudation of a kind of oil, soluble in ether and alcohol. Mr. MacLachlan believes that in the male of Libellula depressa this change of colour does not occur until nearly a fortnight after the metamorphosis, when the sexes are ready to pair. Certain species of N eurothemis present, according to Brauer 51 a curious case of dimorphism, some of the females having their wings netted in the usual manner ;. whilst other females have them "very richly netted as in " the males of the same ~pecies." Brauer " explains " the phenomenon on Darwinian principles by the " supposition that the close netting of the veins is a " secondary sexual character in the males." This latter character is generally developed in the males. alone, but being, like every other masculine character, latent in the female, is occasionally developed in them. vVe have here an illustration of the manner in which the two sexes of many animals have probauly come to resemble each other, namely by variations first appear-· ing in the males, being preserved in them, and then transmitted to and developed in the females ; but in this particular genus a complete transference is occasionally and abruptly effected. Mr. MacLachlan informs me of another case of dimorphism occurring in several species of Agrion in whith a certain number of individuals are found of an orange colour, and these are lil See abstract in the 'Zoological Record' for 1867, p. 450. |