March, 1907.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



-1 



couid be readily examined. Others, accidentally torn, 

 showed the postage stamp fracture with equal distinct- 

 ness. The longitudinal ribs appeared to be externally 

 directed folds or elevations of both membranes. Those 

 on one surface passed around the stem-bearing end of 

 the scale, and were continuous with the corresponding 

 ribs on the other. The perforations ceased at a con- 

 siderable distance from the posterior, or stem end, so 

 that in that region the membranes showed no markings 

 except these ribs, and, in certain instances, several 

 oblique folds or wrinkles. The third membrane was 

 intermediate between the two perforated surfaces, and 

 was structureless. It appeared to be connected with the 

 upper and lower membranes at the front, and at the two 

 lateral margins of the scale. Dr. Stokes adds that its 

 function seemed to be to stiffen and to support the two 

 perforated membranes, which are so exceedingly deli- 

 cate, and so susceptible to injury, that the process of 

 mounting them in balsam had in many instances 

 stripped them from the structureless basement mem- 

 brane, leaving it bare and conspicuous, with only a few 

 perforated fragments scattered over its surface. By 

 analogy, therefore, he endorses Mr. Lctherby's earlier 

 statement as to the perforations in the Podura scale. 



Some years ago I published in Science Gossip (Vol. 

 VII., new series, 1900-1. pp. 152-4) an interesting note 

 on "Podura Scales," by Dr. G. H. Bryan, F.R.S.. 

 originally contributed to the Postal Microscopical 

 Society, in which he suggested that the scales varied so 

 much in fineness that there were probably two varieties 

 of the insect. Dr. Bryan stated that Dr. J. W. Arnold 

 had succeeded in detaching the "exclamation marks/' 

 by means of an electric spark ! (Science Gossip, 1873, 

 p. 40.) He observed further that, in Lcpisma 

 saccharina, there are two kinds of ribs, those running 

 longitudinally, which are on the outer side, and those 

 running radially, which are on the side next the body 

 of the insect; and, by means of a grease-spot on the 

 scale, Dr. Bryan was able to obliterate the longitudinal 

 ribs, whilst the radial ribs remained quite distinct. 

 Where only a little grease was present, also, or at the 

 edge of a grease patch, he observed little air-bubbles to 

 follow the grooves between the longitudinal stria;, thus 

 showing the thickness of the latter. Mr. Beck, in his 

 appendix to Lord Avebury's " Monograph of the 

 Collembola and Thysanura,'' states, however, that the 

 longitudinal markings are on the under side of the 

 scale, whilst the outer side bears the radial markings, 

 the crossing of the two producing a curious optical 

 so as to give the appearance of beads. This optical 

 effect was still more strikingly shown in two scales 

 of Polyonnualus argns, which lay partly over each other, 

 producing an appearance verv similar to that of a 

 coarse Podura scale (see Carpenter's " Microscope," 

 8th edition, pp. 975-980, and Figs. 724, 726, 7^8, and 

 729). In the same volume of Science Gossip (pp. 245 6) 

 I published also' a note by Mr. \V. T. McGhie, in which 

 he described some insect hairs and scales, which seemed 

 to him to exhibit the probable evolution of the insect hair 

 and scale, and stated that "in the nervines a crooked 

 system of vessels is perceptible, and these may he traced 

 right through lo pedicles of the tufts of bristles at the 

 wing's point, the function being, I believe, to supply the 

 scales with the liquid which, according lo Dr. Royston 

 Pigott, is found between the upper and lower mem- 

 branes of the scales. There is certainly, as can be 

 clearly seen with a good objective of wide angle, an 

 intricate system of capillaries feeding ever} pedicle in 

 I he membrane." 



The drawing reproduced on page 70 (Fig. 1 ) shows the 

 appearance of the insect Lepidocy His itself, by 



which it will be seen how it gets its name of ' : spring 

 tail." Fig. 2 is a drawing of a scale of the insect, show- 

 ing the curious watered-silk appearance under low 

 powers or inefficient lenses. Fig. 3 illustrates individual 

 markings on the scale, highly magnified to show the 

 light central stripe. Fig. 4 shows part of a >cale of 

 Lepisma saccharina with the radial markings uppermost, 

 and Fig. 5 one with the longitudinal markings upper- 

 most, whilst Fig. 6 shows the obliteration of the latter 

 by a grease spot on that side. Fig. 7 illustrates Mr. 

 McGhie's suggestions as to the evolution of insect hairs 

 and scales. 



Collecting: Algae. 



In a French scientific journal, M. Gomont gives some 

 instructions to travellers on methods of preparing alga; 

 for an herbarium or for examination. He divides the 

 algae into two groups, those which are visible to the 

 naked eye, and those which are microscopic- in size, and 

 advises the careful labelling of each specimen, with its 

 locality, and the nature of its habitat, as a matter of 

 routine. The whole plant shotdd 1:;- gathered, including 

 its base. Some may be hung on a line in the shade to 

 dry, but more delicate specimens should be laid out on 

 a piece of sized paper, covered with calico, and pr< 

 between sheets of blotting paper, both calico and blot- 

 ting paper being frequently changed to ensure speedy 

 drying. "When the specimens are dry. the calico is 

 removed, and the sheets packed on each other; or 

 the specimens can be floated in sea-w ater. and a piece 

 of paper inserted underneath, when they can then lx> 

 teased out and left on an inclined plane to drain. A 

 solution containing 35 to 40 grammes of salt per litre 

 of water will do if sea-water is not available. Salt may 

 also be used as a preservative, the specimens, after 

 draining, should be packed, in alternate layers of algae 

 and salt, in a stone jar, and the vessel sealed. This 

 method is suitable for a short journey only. 



For microscopic alga-, quick drying in the open air 

 on a sheet of sized paper is host, without calico or 

 pressure. Diatoms and desmids may he placed in a 

 drop of water and allowed to dry naturally. The author 

 discourages the use of liquids for preservation of algae, 

 except for portions of plants which are to be studied 

 anatomically, for which he recommends 90 per cent, 

 alcohol, to which he adds a certain quantity of 

 glycerine or a solution of picric acid. 



Mounting: Mosses. 

 In the Bryologist, Mr. J. I-'. Collins sixes some hints 

 on the mounting of mosses lor the herbarium. Instead 

 of the usual method of pinning the envelopes or pockets 

 to the sheet. In- uses half-inch discs of paper, gummed 

 on both sides, to attach the envelopes, a single wafer 

 being sufficient to hold most envelopes firmly, and being 

 readily detached by a paper-knife. To mount specimens 

 direct upon the sheet, he uses commercial liquid glue, 

 diluted with an equal quantity o\ vinegar or water, 

 which is brushed in a thin layer upon a shex t of glass. 

 Ilk- specimen is rapidly pressed upon this and trans- 

 ferred to its position on the herbarium sheet Small 

 mens, mounted with a certain amount of soil at- 

 tache. I, which gives trouble by crumbling away, are 

 easily hardened by a few diops of diluted white shellac- 

 one part of shellac to three parts of 95 per cent, alcohol. 



nmications and inquiries ."i Microscopical nut! 



addrtsstd to '•'. Skill ' <. " Jersey,' St. Baruabis 



Cambridge. Correspondents an request, ;i spe; : m'ns to be 



nam, 



