WINGS; SOUND-ORGANS 999 



those of the same side are connected together, so as to constitute in 

 flight but one large wing ; this consists of a row of curved booklets 

 on the anterior margin of the posterior wing, which lay hold of the 

 thickened and doubled down posterior edge of the anterior wing. 

 These booklets are sufficiently apparent in the wings of the common 

 bee, when examined with even a low magnifying power ; but they 

 are seen better in the wasp, and better still in the hornet. The 

 peculiar scaly covering of the wings of the Lepidoptera has already 

 been noticed ; but it may here be added that the entire wings of 

 many of the smaller and commoner insects of this order, such as the 

 Tineidce or ' clothes-moths,' form very beautiful opaque objects for 

 low powers, the most beautiful of all being the divided wings of 

 the Fissipennia or ' plumed mot?hs,' especially those of the genus 



us}- 



There are many insects, however, in which the wings are more or 

 less consolidated by the interposition of a layer of horny substance 

 between the two layers of membrane. This plan of structure is 

 most fully carried out in the Coleoptera (beetles), whose anterior 

 wings are metamorphosed into elytra or ; wing-cases ; ' and it is 

 upon these that the brilliant hues by which the integument of many 

 of these insects is distinguished are most strikingly displayed. In 

 the anterior wings of the Forfoulidce, or earwig tribe, the cellular 

 structure may often be readily distinguished when they are viewed 

 by transmitted light, especially after having been mounted in Canada 

 balsam. The anterior wings of the Orthoptera (grasshoppers, 

 crickets, &c.), although not by any means so solidified as those of 

 Coleoptera, contain a good deal of horny matter ; they are usually 

 rendered sufficiently transparent, however, by Canada balsam to be 

 viewed with transmitted light ; and many of them are so coloured 

 as to be very showy objects (as are also the posterior fan-like wings) 

 for the electric or gas microscope, although their large size and the 

 absence of any minute structure prevent them from affording much 

 interest to the ordinary microscopist. We must not omit to men- 

 tion, however, the curious sound-producing apparatus which is 

 possessed by most insects of this order, and especially by the common 

 house-cricket. This consists of the ' tympanum,' or drum, which is 

 a space on each of the upper wings, scarcely crossed by veins, but 

 bounded externally by a large dark vein provided with three or four 

 longitudinal ridges ; and of the ' file ' or ' bow,' which is a transverse 

 horny ridge in front of the tympanum, furnished with numerous 

 teeth ; and it is believed that the sound is produced by the rubbing 

 of the two bows across each other, while its intensity is increased 

 by the sound-board action of the tympanum. The wings of the 

 Fidyoridce (lantern- flies) have much the same texture as those of the 

 Orthoptera, and possess about the same value as microscopic objects, 

 differing considerably from the purely membranous wings of the 

 Cicadce and Aphides, which are associated with them in the order 

 Nomoptera. In the order Hemiptera, to which belong various kinds 



1 Compare the recently published memoir by M. Baer, ' Ueber Bau und Farben 

 der Fliigelschuppen bei Tagfaltern,' in Zeitschr.f. wiss. Ziiol. Ixv. (1898), pp. 50-65, 

 as also M. von Linden on the development of the markings, pp. 1-50 of the same volume. 



