SCALES 



979 



I 1 



membranes, probably a deposit on the interior surface of one or both 

 of them. 1 



Although the Podivridce and Ltpismidce now rank as distinct 

 families, yet they approximate sufficiently in general organisation, 

 MS well as in habits, to justify the expectation that their scales 

 would be framed upon the same plan. The Poduridce are found 

 amidst the sawdust of wine-cellars, in garden tool-houses, or near 

 decaying wood, and derive their popular name of ' spring-tails ' 

 from the possession by many of them of a curious caudal appen- 

 dage by which they can leap like fleas. This is particularly 

 well developed in the species now designated Lejndoci/rtus curvi- 

 collis, which furnishes what are ordinarily known as ' Podura ' scales. 

 * When full grown and unrubbed,* says Sir 

 John Lubbock, ' this species is very beauti- 

 ful, and reflects the most gorgeous metallic 

 tints.' Its scales are of different sizes and 

 of different degrees of strength of marking 

 (fig. 728, A, B), and are therefore by no 

 means of uniform value as tests. The 

 general appearance of their surface, under 

 a power not sufficient to resolve their mark- 

 ings, is that of watered silk, light and dark 

 bands passing across it with wavy irregu- 

 larity ; but a well-corrected objective of 

 very moderate aperture now suffices to re- 

 solve every dark band into a row of dis- 

 tinct ' exclamation marks.' A certain 

 longitudinal continuity may be traced be- 

 tween the ' exclamation marks ' in the 

 ordinary test scale ; but this is much more 

 apparent in other scales from the same 

 species (fig. 729), as well as in the 

 scales of various allied types, which were 

 carefully studied by the late Mr. R. Beck. 2 

 In certain other types, indeed, the scales 

 have very distinct longitudinal parallel 

 ribs, sometimes with regularly disposed 

 cross-bars ; these ribs, being confined to one 

 surface only (that which is in contact with 

 the body), are not subject to any such interference with their optical 

 continuity as has been shown to occur in Lepisma ; but more or less 

 distinct indications of radiating corrugations often present them- 

 selves. The appearance of the interrupted ' exclamation marks ' 

 Mr. J. Beck considers to be due ' to irregular corrugations of the 

 outer surface of the under membrane, to slight undulations on the 

 outer surface of the upper membrane, and to structure between the 

 superposed membranes.' It has, indeed, been stated by Mr. Joseph 



1 See Mr. Joseph Beck in Sir J. Lubbock's Monograph, p. 255. 



2 Trans. Microsc. Soc. n.s. vol. x. 1862, p. 83. See also Mr. Joseph Beck, in the 

 appendix to Sir John Lubbock's Monograph, and in Monthly Microscopical Journal, 

 iv. p. 253. 



3 K 2 



FIG. 727. Scale of Machilis 

 polypoda. 



