The Descent of Man

with splendid green, blue, yellow, and vermilion
metallic tints; and the sexes often differ.
Thus, as Prof. Westwood remarks (50. 'Modern
Classification,' vol. ii. p. 37.), 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 Ramburii these
colours are exactly reversed in the two sexes.
(51. Walsh, ibid. p. 381. I am indebted to this
naturalist for the following facts on Hetaerina,
Anax, and Gomphus.) In the extensive N. American
genus of Hetaerina, 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