INSKCTS AM) AKACHNIMA. 



furnished at one end with a sort of handle r * pedicle ' (Figa. 414, 415), 

 b\ which it is lilted inio ;i ininule socket ;ill:iched to the surface of the 

 insect; and on the wind's of I .efiidofileni these sockets are so arranged 

 that the scales lie in \<T\ revn lar ro\\ s, each ro\v overlapping a, portion 

 of the next, so us to give to their siirl'ace, when sullicienlly magnified, 

 \er\ much the appearance of being lilt'tl like the roof of a. house. Such 

 an arrangement, is said to he ' imbricated.' The forms of these scales are 

 ofleii \er\ curious, and frequently difTor a good deal on Hie severa,! parts 

 of the wings and of the body of the same individual; being iisually more 

 expanded on the former, and narrou er and more hair like on the latter. 

 A peculiar type of scale, which has been disl inguished by the designation 

 j>/i/nin/t', is met with :miong the /'ieridir. one of the principal families 

 of (he hiurnal Lepidoplera. The * plumules ' :i re not Hat, but cylin- 

 drical or bellows-shaped, and are hollow; they are at (ached to tllO wing 

 h\ a hull), :it the cud of a- thin elastic peduncle thai ditl'ers in length in 

 dilTcrcnl species, a.nd proceeds from the liroadcr, not, from the narrower 

 end of the scale; whilst, (he free extremity usually tapers oil', and cud: 

 in a, kind of brush, (.hough sometimes i( is broad and has its cdi'e fringed 

 with minute lilanients. r rhcso 'plumules/ which are peculiar to the 



males, are found on the upper surface of the win^s, partly between and 

 partly under (he ordinary scales. They seem to he represented amon^ 

 the /. //r<r// i</<r hy (he ' ha-t I Icdore ' scales to he presently described 



(eai/.' 



rM(>. 'The ncculiar markin-s exhibited by many of these Scales, very 

 early allracicd Mie al.tenl ion of <>plici:,,ns onga^ed in I he application of 

 Achromatism to (he Microscope (i< !.">); for, as ( he cleai'iiess and strength 

 wilh which (hey could be shown, were found to depend on the decree (o 

 which the angular aperture of lin Objective could ho opened without sac 

 rilice of perfect correction for .spherical and chroma! ic. aJterrat ion, HlUJh 

 scales proved very serviceable as ' (cs(,s.' The Author can well remember 

 the time when those of Mnr/t/in inrtu'/dH.t ( Ki^. -Ill), (he ordiiiai-y and 

 ' hat t ledore ' scales of the j^i/i/o/tn/io/ us tin/its (l^i^'s. -ll. r ), -ll'i), and the 

 scales of the /,{'/H'XHHI- Mtirlntriint ( V\^. -Mi), which are now only used 

 for lest in:; Objectives of /tun or -medium power ( I.V.>, I., II.), were the 

 recognized tests for objectives of ///V///. power; while (ho exhibition of 

 alternating lighl, and da,i'k bands on a, l*o<h<rn scale was regarded US 11 

 lirsl-rale performance. The resolution of these bands into tho ' notes of 

 admiration' (Plate II., tig. "2) now clearly shown by every good 'Stu- 

 dent's' I Ith, marked tho next, step in advance; and I bough the intro- 

 duction of the I >iatom-tesls greatly promoted the enlargement of angular 

 aperture, yet the Author has Mm authority of the ablest, constructors of 

 high-power Objectives in (bis county for stating, (hat (hey still regard 

 the Tod lira-scale as the best lest for definition, and consequently for that 

 nf ion of ipialities which is most required in Objectives (o be used 



for l-iiological investigations of tlio greatest dillieulty ($ l. r S, YiA a As 

 the real structure of this scale, of which the ' notes of admiration, or the 

 'exclamation-markings' constitute the optical expression, has been a 

 mailer of much controversy, the question requires special consideration; 



'See Mr Watson's Memoirs 'On the Scales of Battledore Butterflies,' in 



" Monthly Microseo|)ical Journal." Vol. ii., pp. T.\, :U-I. 



'The Author is assured that it is hy no means an uncommon experience, on 

 liist putting together tin Ohjeetivo of wiclo aperture, to lind it capahle of resol\ 

 ing a dilliciilt Diatom, whilst, when tested on a Podura-xcale, it utterly fails, Oil 

 ueeount of its imperfect ' deli nil ion." 



