Chap. X. NEUEOPTEKA. 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 sub- 

 families, 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 Neurothemis 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 species." 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. 

 We have here an illustration of the manner in which 

 the two sexes of many animals have probably 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 occa- 

 sionally and abruptly effected. Mr. MacLachlan in- 

 forms me of another case of dimorphism occurring in 

 several species of Agrion in which a certain number of 

 individuals are found of an orange colour, and these are 



51 See abstract in the 'Zoological Record ' fur 18G7, p. 4^0. 



