290 The Descent of Man. Part L . 



Order, Neuroptera. — Little need here be said, except as to 

 colour. In the Ephemeridse the sexes often differ slightly in 

 their obscure tints; 49 but it is not probable that the males are 

 thus rendered attractive to the females. The Libellulidse, or 

 dragon-flies, are ornamented with splendid green, blue, yellow, 

 and vermilion metallic tints ; and the sexes often differ. Thus, 

 as Prof. West wood remarks, 50 the males of some of the 

 Agrionidae, " are of a rich blue with black wings, whilst the 

 " females are fine green with colourless wings." But in Agrion 

 Barnburii these colours are exactly reversed in the two sexes. 51 

 In the extensive N. American genus of Hetserina, the males alone 

 have a beautiful carmine spot at the base of each wing. In 

 Anax Junius the basal part of the abdomen in the male is a vivid 

 ultramarine blue, and in the female grass-green. In the allied 

 genus Gomphus, on the other hand, and in some other genera, 

 the sexes differ but little in colour. In closely-allied forms 

 throughout the animal kingdom, similar cases of the sexes 

 differing greatly, or very little, or not at all, are of frequent 

 occurrence. Although there is so wide a difference in colour 

 between the sexes of many Libellulidse, it is often difficult to say 

 which is the more brilliant ; and the ordinary coloration of the 

 two sexes is 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. Mr. MacLachlan, who has closely 

 attended to this family, writes to me that dragon-flies— the 

 tyrants of the insect-world — are the least liable of any insect to 

 be attacked by birds or other enemies, and he believes that their 

 bright colours serve as a sexual attraction. Certain dragon-flies 

 apparently are attracted by particular colours : Mr. Patterson 

 observed 02 that the Agrionidse, of which the males are blue, 

 settled in numbers on the blue float of a fishing line ; whilst two 

 other species were attracted by shining white colours. 



It is an interesting fact, first noticed by Schelver, that, in 

 several genera belonging to two sub-families, the males on first 

 emergence from the pupal state, are coloured exactly like the 

 females; but that their bodies in a short time assume a con- 

 spicuous 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. 



19 B. D. Walsh, the ' Pseudo-neu- indebted to this naturalist for the 



roptera of Illinois,' in ' Proc. Ent. following facts on Hetserina, Anax, 



Soc. of Philadelphia.' 1862, p. 361. and Gomphus. 



40 ' Modern Class/ vo'i. ii. p. 37. "'Transact. Ent. Soc' vol. i. 



11 Wa'jh, ibid. p. 381. I am 1836, p. lxxxi. 



