July, : 



KNOWLEDGE & SCIENTIFIC NEWS. 



i6^ 



Rosenhain for mounting specimens of irregular shape, such as 

 sections of metals, so that the polished surface to be examined 

 was normal to the optic axis of the microscope, thus obviating 

 the necessity for a levelling stage. .\ third exhibit consisted 

 of troughs, invented by Mr. T. G. Kingsford, suitable for fluids 

 for light filters, or for examining aquatic life. They were con- 

 structed in various sizes of two flat discs of glass, such as were 

 used for modern clocks, clipped round the edges by a thin 

 metal band, leaving a suitable opening at the top. The band 

 is drawn tight by means of screws near the ends, leakage 

 being prevented by a lining of rubber strips. These tanks can 

 be readily taken to pieces for cleaning, and will withstand 

 sudden changes of temperature. .\ note by Mr. A. A. C. 

 Eliot Merlin on Mr. \elson"s new formula amplifier was read. 

 The amplifier consists of a negative lens placed in the rear of 

 the objective, and was calculated by Mr. Nelson for the author. 

 to enable him to make some delicate microscopical measure- 

 ments. With the usual arrangement of a low-power eyepiece 

 and screw micrometer, the magnification atTorded by high- 

 power objectives was insufficient to ensure accuracy in .all 

 cases, and it was not desirable to use more powerful eyepieces 

 as the spider lines then appeared too coarse. The author 

 found the amplifier yielded especially good results when used 

 for micrometrical purposes, and he suggested its application 

 to students' microscopes for quickly obtaining an increase of 

 magnifying power. Mr. Xelson's formula for the amplifier 

 was given. .\ note on Grayson's 120,000 Band Plate, by Mr. 

 Nelson, was then read. "The band was resolved strongly 

 by an apochromatic oil immersion J-inch, i'43 N.A., and a 

 5 ej'cpiece. It was also resolved by a semi-apochromatic 

 j,7-inch, I-3 N..-\., and 5 eyepiece, and by an old achromatic 

 water immersion ^V-inch, f2 N..\., but in the last case the 

 lines appeared to have irregularities. The 90,000 band was 

 resolved by an apochromatic |-inch, "96 N.A., with some difli- 

 cultj'. The author remarked that the latest books on physical 

 optics state that -p~5^-i;-inch is the theoretical limit for micro- 

 scopical vision. Mr. Nelson stated that ruled lines are more 

 difficult to resolve than diatoms of equal fineness. He said 

 the best screen is made from a saturated solution of acetate 

 of copper, many times filtered, lo which a very small ((uantity 

 of methylen blue should be added. Sunlight with a Heliostat 

 was used, and the light made oblique in one azimuth. The 

 theoretical resolving limit for oblique light may I'oughly be 

 taken at 100,000 times the N.A. of the objective. Dr. Hebb 

 remarked that when this plate was exhibited at the Royal 

 Society's Conversazione some of the lines, though resolved, 

 appeared weaker than others. Mr. E. E. Hill said this was 

 due to the objective used having an aperture of only fi N.A. 

 Mr. Conrad Beck exhibited some flower seeds. 



Quekett Microscopical Club. 



The 414th ordinary meeting of the Club was held on 

 May 20, at 20, Hanover Square, W., the President, Dr. E. J. 

 Spitta, V.P.R.A.S., in the chair. Mr. H. Wallis Kew, F.Z.S., 

 gave an interesting account of the False-Scorpions or Chelifers, 

 illustrating his description with a number of lantern slides. 

 The Chelifers, or lobster mites, as they are popularly called, 

 form a distinctive though little studied Order of the Arachnida. 

 They have been known to science ever since the time of 

 Aristotle, who classed them with the true Scorpions, a mistake 

 which was perpetuated for over 2000 years. Of retiring habits 

 and minute size they may be found in all quarters of the world 

 in suitable places. Shunning the light they conceal them- 

 selves under bark, or among mosses and dead leaves, where 

 they lie motionless until their prey wanders within the reach 

 of the terrible pedi-palps or forcep-like claws of the second 

 pair of appendages, which instantly close on the victim, and 

 transfer it to the cheUcerae, the smaller forceps near the 

 mouth, by which the victim is held while the juices are sucked 

 out. 



Mr. Kew referred at some length to the habit, peculiar to 

 this Order, of attaching themselves by the forceps to the legs 

 of other insects, by which they are transported from one place 

 to another. Sometimes more than one Chelifer is found on 

 the same insect, and there are recorded instances of as many 

 as six, eight, and ten being found so attached. The habit has 

 been known for over a century and has been recorded from 

 ever}' quarter of the world, but its object is still one of the 

 puzzles of science. They do not appear to be parasites, and 

 the fly appears too large to be a victim, so it has been sug- 



gested that they are merely stealing .1 ( In- ip 1 ulr .11 iIh ilys 

 expense. 



Mr. 1). J. Scourfield then gave a description of .Apstein's 

 Ouautitativo Plankton Net, which liad been devised for the 

 determination of the exact (piautity of organic life in a given 

 volume of water. The net h.id been used successfully on the 

 .Scotch lochs, and a specimen net, with photographs showing 

 the method of use, was exhibited to the members. 



Daphnia and Vorticella. 



Mr. Caffyn.of llnrnscy, writes : " I have recently collected 

 a qu.antity of the Great Water h'lea at Dorking, and practically 

 every one of them is covered with Bell Animalcules. I think 

 these are chiefly K/'is/v/is, but there are a few I 'or/uv/Ar. In 

 Points and Rock Pools. Mr. Henry Scherren says, on page 157, 

 that it has been stated that thecommtm water-flea never bears 

 about with it any of the Bell Animalcules that flourish so 

 luxuriantly on the Cyclo/'S P.; this is stated to be due to a 

 slimy film. Mr. Scherren goes on to state that he does not 

 know as to the film l)eing there or not, but he thinks plenty of 

 the Dciplinia could be found bearing those Vortici-llidans, and 

 he s.iys that he has lieen told by pond-hunters that they have 

 seen them in this state. I do not know if the matter has been 

 definitely proved before ; if not, 1 can certainly verifv it now." 



Notes and Queries. 



W. N. Bone, Hove. 



I am glad that Mr. Warburton's articles on Mites have 

 decided you to take up the definite study of the Acari. There 

 is so much work to be done here that is well within the powers 

 of anyone who is interested in the subject. L'nfortunately, 

 the literature of the Acari is in a very unsatisfactory and in- 

 complete slate, and I am afraid I can give you no useful 

 references other than those mentioned in the articles referred 

 to. You will find the pages devoted to the subject in •' Car- 

 penter " useful as a beginning, however. The articles on 

 Spiders and Mites in the forthcoming volume of the Cambridge 

 Natural History are contributed by Mr. Warburton, and are 

 now in the Press. With regard to killing the very smallest speci- 

 mens, Mr. Warburton tells me that there is nothing better 

 than boiling water, and that yon must try to straighten the 

 legs with a camel-hair brush, under a lens. He says chloro- 

 form increases this ditticulty. 

 J. C. Miller, Wlllesden. 



.As far as I can gather from your description and drawing, 

 the infusorian referred to must surely be the common Ptira- 

 nia-cinm, or "slipper animalcule." Its length is generally 

 about 200 to 260 M (m = 'ooi millimetre, and is the standard 

 of microscopical measurement). It is of a very much lower 

 order of life than Hydra, and is really unicellular, though the 

 radial striations of the pronounced cortex give it a nuflti- 

 cellularlike appearance. There is therefore no definitely 

 marked-otf body cavity or enteivn, ihoap^h. it has a "buccal 

 groove" which leads into a fairly definite mouth, but this 

 communicates direct with the semi-fluid protoplasm within. 

 There is a large nucleus, and a smaller luicronucleus, and two 

 contractile vacuoles, which you may have mistaken for eyes. 

 When feeding, the animalcule swallows with a sort of gulp, 

 which carries the particle of food inwards enveloped by a globule 

 of water, which is gradually absorlx-d later, and any remaining 

 particles subsequently ejected at a soft place in the cortex, which 

 may be looked upon as a potential though not a true or 

 actual anus. It is probably this enveloping globule of water 

 and the curiously sudden nu^thod of swallowing that you have 

 mistaken for a " bag." I am sorry to have left your question 

 so long unanswered, but it has been due to circumstances 

 beyond my control, as explained last month. 

 Mlcro-Funjti for Distribution. 



By the kindness of Mr. C. H. Caffyn, of Hornsey, I am able 

 to offer a limited quantity of specimens of micro-fungi, mostly 

 named, suitable for mounting as opaque objects. Those wish- 

 ing to avail themselves of this offer should apply without delay, 

 utilising and complying with the terms of the coupon to be 

 found in the advertisement pages of the current issue of this 

 magazine. 



'Communications and enquiries on Microscopical matters are invited, 

 and should he addressed to F . SItillington Scales, "Jersey," St. 

 Ilariiabas Road, Cambridge.] 



