SCALES OF INSECTS. 



657 



Fig. 335. 



513. Among the most beautiful of all these Scales, both for 

 colour and for regularity of marking, are those of the Butterfly- 

 termed Morpho Menelaus (Fig. 334). These are of a rich blue 

 tint, and exhibit strong longitudinal strise, which seem due to 

 ribbed elevations of the superficial coloured layer. There is also 

 an appearance of transverse striation, which cannot be seen at all 

 with an inferior Objective, becomes very decided with a good Ob- 

 jective of medium focus, but is found, when submitted to the test 

 of a high power and Achromatic Condenser, to depend upon a sort 

 of beaded subdivision of the longitudinal ribs ; the transverse striae 

 that may be seen between these ribs being apparently produced by 

 the beading of the ribs on the other surface of the scale. — The 

 large Scales of the Polyommatus argus (Azure-blue Butterfly) 

 resemble those of the Menelaus in form and structure, but are 

 more delicately marked. The same Insect, however, furnishes 

 small Scales, which are commonly termed the ' Battledoor ' scales, 

 the resemblance which their form presents to that instrument 

 being usually much greater than in the specimen represented in 

 Fig. 335 ; these scales, also, are marked by narrow longitudinal 

 ribbings, which at intervals expand into 

 rounded or oval elevations that give to 

 the scale a dotted appearance ; at the 

 lower part of the scale, however, these 

 dots are wanting; and in the interval 

 between the two portions, we observe a 

 sort of crescent, formed of minute pig- 

 ment-granules, crossing the scale trans- 

 versely. — The Scales of the Pontia 

 brassica (Cabbage-Butterfly) and of the 

 Hipparchia janira (Meadow-brown But- 

 terfly), have longitudinal markings of a 

 somewhat similar nature, but less sharply 

 defined ; these are further noticeable for 

 the brush-like appendage which each 

 scale bears at the end furthest from its 

 implantation. — Although scarcely useful 

 as a ' Test-object,' since its structure is 

 too easily resolved, the Scale of the 

 Lepisma saccharina or ' Sugar-Louse' 

 deserves notice; the longitudinal ribbings 

 being so strongly marked and so regular, 

 rising at intervals into tooth-like pro- 

 jections, as to give them an appear- 

 ance resembling that of many Bivalve Shells. The long narrow 

 Scale of the common Gnat, also, exhibits a few very prominent 

 straight-edged ribbings ; and from its small size, it serves as a 

 good Test-object for the medium powers.— The Podura plumbea 

 or ' Spring-Tail ' is a little wingless Insect that is occasionally 



v v 



Battledoor Scale of 

 Polyommatus argus 

 (Azure-blue). 



