i5 2 



SCIENCE-GOSSIP. 



EXTBACTS FE0M POSTAL MICROSCOPICAL 

 SOCIETY'S NOTE-BOOKS. 



[Beyond absolutely necessary editorial revision 

 these notes are printed as written by the various 

 members, without alteration or amendment. Cor- 

 respondence on these notes will be welcomed. — 

 Ed. Microscopy, S.-G.] 



NOTES, by Dr. G. H. Bryan, F.R.S. 



Podtjra and other Scales.— Although " scales 

 of Lepisma " and " scales of Podur.a" find a place in 

 most cabinets, I do not remember a series of 

 objects of this class having been circulated round 

 the P M.S., and I venture to hope that the present 

 series may afford some instruction to some of the 

 members, and perhaps stimulate them to collect a 

 few of these interesting little objects for them- 

 selves. 'J he " Podura scale " seems to have pro- 

 duced a great sensation among microscopists about 

 1S73, when it was brought before our notice by the 

 late Mr. Beck ; but since then fresh " test objects " 

 have superseded it to a large extent— viz. Plexiro- 

 s'gma angulatum, and then An iplii pleura pellucida, 

 and these seem to have gradually led to the im- 

 provement in lenses required for the study of 

 bacteriology. At the same time these old test 

 scales are still worthy of attention. About the 

 time of their popularity Sir John Lubbock wrote a 

 ' : Monograph of the Collembola and Thysanura," pub- 

 lished by the Ray Society in 1872, and in the same 

 year Mr. S. J. Mclntyre contributed a paper on 

 them to Science-Gcssip for December 1872 and 

 January 1873. Sir J. Lubbock's book contains a 

 valuable appendix on the scales of these insects 

 by Joseph Beck, illustrated by fine lithographic 

 plates from drawings by his brother, the late 

 Richard Beck. Lcphlocyrtus curvicollis. — Scales 

 of this insect are often seen in old collections 

 labelled " Podura pluvibea," although the generic 

 name Podura is now given to an insect without 

 scales, and plumbea is the specific name of almost 

 the only one of the Collembola whose scales do not 

 show the familiar " marks of exclamation." This 

 is one of the largest species of the genus, and 

 when alive looks darkish. This slide is best 

 examined without the cover on, for which purpose 

 the central part of the ornamental paper is not 



.— v, ■■ "•••'•• A _ 



Fig. 1. Movable Cover-glass. 



gummed down. To. remove the cover, carefully 

 insert a slip of thin card or note-paper under 

 the edge of the green paper at one side and 

 push the cover out at the other; replace in the same 

 way when done with (see fig. 1). If the cover 

 breaks, a fresh one can be inserted. This is really 

 an excellent device for mounting dry objects, and 

 is worth remembering. Note the saltatory append- 

 age from which the name "spring-tail" is derived ; 

 also the curious humpback projection of the thorax 

 characteristic of the genus Lepidot yrtus.irom which 

 the specific name curvicbllis is derived (fig. 9). 

 L. curvicollis seems to have two varieties, charac- 



terised by differences in their scales, which are 

 called "ordinary" and " test " scales. (') Fig. 10 

 shows scales which I believe to be test scales ; 

 the markings are bolder, less continuous, and, 

 when properly focussed, each shows a more distinct 

 bright line down the middle (see fig. 2). The 

 " notes of exclamation " are thus more easy to 

 show up separate and distinct than in the ordinary 



Figs. 2-8. Markings on various Scales. 



scale. When mounted in balsam the marks become 

 almost, if not quite, invisible. Dr. J.W. Arnold 

 succeeded in dataching the " exclamation marks " 

 by means of an electric spark. [See Science- 

 Gossip, 1873, p. 40.] Lepidocyrtus violareus, a 

 smaller species than curvicollis, which, like that 

 insect, is abundant in our cellars. — I refer, with 

 some doubt, to this species. Both that and the 

 previous kind seem to congregate under or about 

 a sheet of paper placed in the cellar, especially if 

 a little flour has .been sprinkled on it. I think 

 they like the shelter, and dislike light. The scales 

 are more irregular in shape and the markings 

 finer, but the lines of marks are wider apart (see 

 fig. 3); and although the marks are more 

 continuous, their heads are rather more bulbous 

 than in L. curvicollis. Beclda argentea is a silvery 

 little insect, far smaller than either of the pre- 

 ceding and much lighter in colour, which I 

 found in considerable numbers running about 

 stones on a wall at Colwyn Bay at dusk, when 



(\) Students of these scales can purchase tlifm at the 

 opticians', but they are unfortunately becom ng increasingly 

 difficult to procure. A slide of the "test '' Podura only should be 

 asked for, mounted dry. Under the microscope the coarser 

 scales and those actually in contact with the cover-glass should 

 be examined. In this latter case the removal of the cover-glass, 

 with its manifest dangers, is not necessary. The Podura scale, 

 on account of its variability, is not a trustworthy guide to the 

 testing of lenses in unskilled bands, and we put no faith in the 

 exhibition of the inner markings, on which so much strfss is 

 1 iid. They are easily shown by an indifferent lens with a little 

 " stopping down " of the diaphragm, and we believe them to he 

 caused by an optical effect of diffraction. The true nature of 

 the markings on a Podura scale lias, however, not yet been satis- 

 factorily explained. — En. Microscopy. 



