19060 189 



were without doubt the unknown female of midipalpis, an insect 

 as common with me as unispinosn. A<,^ain, Becker ascribes both yellow 

 and black halteres to opacn^ or rather perennis as Mr. Collin has 

 pointed out to me our insect should be called. In my own series were 

 representatives of bi)th forms, but the yellow halteres were always 

 associated with one set of characters and the black with another set, 

 leavintr little doubt that the two forms were two distinct species. 

 There is, however, one insect, the abundant concinna, in which there 

 is great irregularity in this respect. Our author was of opinion that 

 the variation depended upon sex, black halteres going with the male 

 and yellow halteres with the female. But in my experience it is a 

 matter of perfect indifference, each sex having them sometimes one 

 colour and sometimes the other. 



It is perhaps worth noting that there seems to be no definite 

 relation between the colour of the halteres and the general colour of 

 the insect. Frequently the relation is just the reverse of what would 

 have been expected, that is to say, in two closely related species, such 

 as unispinosa and nudipalpis, the lighter coloured insect will have the 

 darker halteres and vice versa There is, however, a still more curious 

 instance of cross colouring in the PhorldcB, which cannot fail to strike 

 the observer. The wings are commonly tinged with some shade of 

 yellow, brown or grey, but sometimes they are perfectly clear and 

 diaphanous. Now these diaphanous wings always occur in black 

 species, and usually in the very blackest, whilst I cannot call to mind 

 a single instance of such wings among the light coloured, yellow or 

 red species; on the contrary, in them these organs are often especially 

 deeply tinted. The rule too holds good equally between the varieties 

 of a species as between species themselves. Thus, the type form of 

 pygmcea in Group II is a dark insect with clear wings, but its light 

 coloured variety, hrachyneura^ has them deeply tinged with yellowish- 

 brown. 



A word as to some of the terms and characters employed. The 

 short veins which run into the costa are called the " thick " veins 

 and the long ones coursing over the wings the " thin " veins, 

 names which Mr. Verrall has already familiarised us with. In enume- 

 rating the costal divisions or segments the basal division formed by 

 the cross vein is left out of account, since it has no differential sig- 

 nificance ; hence the recognised divisions are only two or three in 

 number, according as the second thick vein is simple or forked. The 

 anal " protuberance" is exclusively a character of the male sex. It 

 is the outlet of the intestinal canal and lies just underneath the dorsal 



