SEXUAL SELECTION 381 



carmine spot at the base of each wing. In Anax Junius the 

 basal part of the abdomen in the haale 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 color. In closely allied forms 

 throughout the animal kingdom, similar cases of the sexes 

 di£Eering greatly, or very little, or not at all, are of frequent 

 occurrence. Although there is so wide a difference in color 

 between the sexes of many Libellulidae, it is often difficult 

 to say which is the more brilliant ; and the ordinary colora- 

 tion of the two sexes is reversed, as we have just seen, in 

 one species of Agrion. It is not probable that their colors 

 in any case have been gained as a protection. Mr. Mac- 

 Lachlan, 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 colors 

 serve as a sexual attraction. Certain dragon-flies apparently 

 are attracted by particular colors. Mr. Patterson observed'' 

 that the Agrionidse, of which the males are blue, settled 

 in numbers on the blue float of a fishing line, while two 

 other species were attracted by shining white colors. 



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 colored exactly 

 like the females; but that their bodies in a short time 

 assume a conspicuous milky-blue tint, owing to the exuda- 

 tion of a kind of oil, soluble in ether and alcohol. Mr. Mac- 

 Lachlan believes that in the male of Libellula depressa this 

 change of color does not occur until nearly a fortnight after 

 the metamorphosis, when the sexes are ready to pair. 



Certain species of Neurothemis present, according to 

 Brauer,*' a curious case of dimorphism, some of the females 

 having ordinary wings, while others have them "very 

 richly netted, as in the males of the same species." 



6S "Trans. Ent. Soe.," vol. i., 1836, p. Ixxxi. 



" See abstract in the "Zoological Record" for 1861, p. 450. 



