INSECT VARIETY. 85 



again are present on feather scales, the homolog'iies of those that 

 clothe the wing-membrane in Lepidoptera. The interferential 

 colours of the green Diamond Beetle {Entimus) are ascribed to 

 these scales, which possess a laminated surface similar to what 

 we find in mother-of-pearl; elsewhere, a play of colour in 

 Coleoptera is imputed to a similar integumental modification.^ 

 Rarely are colours and patterns of beetles sexual; some lamel- 

 licorns and long-icorns may be adduced as example, nevertheless, 

 and among the former we find the glistening Hoplia canda with 

 a male bright blue and a black female. 



The posterior alar organs of grasshoppers and bugs are often 

 colourless; those of beetles, I believe, are universally so; and as 

 we descend the chromatic scale, we witness in the membraneous 

 wing-groups of diurnal Neuroptera, Hymenoptera, and Diptera 

 pure colour and patterns still less marked on the alar organs, 

 while these acquire often prominence on their bodies which 

 assume a maximum brilliancy. Yet even here exceptional cases 

 occur where alar colouring, protective or attractive, extends to 

 the wings, and is there even sexually marked, as, for instance, in 

 flies of the genus Bolichopus (Plate V., Fig. 1), where the male 

 has black wing-tips ; or the Dragon-flies of the genus Calopteryx, 

 where the male has bluish organs of flight. In the Dragon-flies, 

 again, as a group, males are not unfrequently distinguished by 

 bright primitive tints, as for example — 



. f Abdomen of male red, 1 Libellula ferruginea. 



I in female olivaceous J ,, sanguinea. 



•p r Abdomen of male blue, 1 Libellula depressa. 



L in female olivaceous J ,, c^rulescens. 



p [ Abdomen of sexes discriminated 1 ^schnina. 



I by lines and spots J Agrion. 



With bees, as flies, bright colouring of the abdomen is uni- 

 versal, and it is either resident in the dermis or diversifies a 

 covering of hairs ; having in the first instance often a metallic 

 lustre. The humble bees present likewise sexes differentiated 

 by markings, and in the ease of Anthophora retusa we have a 

 male bee black, with an orange female ; this of course refers to 

 abdominal colouration. 



* The play of colours on a Dove's neck is due to a bead-like thickening of 

 the fibrils, and not to impressions, as has been stated. 



