Oct., 1904.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



251 



hatched female is found to have ovarian tubes in which 

 are eggs in various stages of development. The 

 youngest appear as oblong protoplasmic masses in the 

 tube ; later each of these masses in the chain becomes 

 constricted in the middle ; this becomes more 

 accentuated, until the egg assumes a dumb-bell shape, 

 the two parts being connected by a narrow neck, on 

 which there is a curious papillated valve or lip. Be- 

 fore this egg is laid in the Coccid host, one division 

 disappears, so that the egg as found in the host is an 

 oval body with a stalk which is found to iun to the sur- 

 face of the host's carapace, where its mouth is plugged 

 with some dark substance. The position of the para- 

 site egg is constant, being always dorsal and 

 posterior, a little to the left. In an allied form, 

 Encyrlus fiisicollis. Professor Marchal, of Paris, has 

 found that each egg gives rise to upwards of a hundred 

 embryos — the host being a caterpillar. 



The larva; of Comys mfeltx passes through various 

 curious and complex conditions, peculiar chiefly for the 

 means it adopts for breathing ; the most startling being 

 that of the prepupa, where the host trachea' appear to 

 be themselves utilised and connected with the parasite 

 spiracles, and respiration goes on with the aid of these 

 borrowed tubes. Another curious feature is that the 

 prepupa seems to evolve a modification of the 

 Malpighian tubules of the larval form, and to get rid of 

 its spare uric acid in sacs containing rosettes of red 

 uric acid crystals, these sacs being applied to the sides 

 of the parasite's body, and left behind on the old pupal 

 skin when the fly escapes. 



{To be concluded.) 



NeNvton's Rings in Microscopica.1 

 Objectives. 



A Correspondent sends the following note : — 



" The modern method of testing optical curves on 

 glass to ascertain that they are accurately formed is by 

 means of what is known as proof plates. These proof 

 plates are made of glass, having ground and polished in 

 them the precise curve required. When the lens is 

 finished, the proof plate is put in contact with it, and if 

 the two are coincident — i.e., the two surfaces of the lens 

 and the proof plate respectively make optical contact — 

 coloured rings, known as Newton's Rings, will be seen. 



" For immersion objectives used on the microscope, 

 the full power of the objective can only be developed 

 when specimens are mounted either in a medium of suit- 

 able refractive index, or are actually adherent, and in 

 optical contact with the under side of the cover glass. If 

 a slide of the diatom Pleurosigma angulatum be searched 

 over with a lens, say, of i-in. power and a deep eyepiece, 

 specimens will be found on which coloured rings — some 

 round, some elliptical, others of a nondescript shape — 

 will be seen, and it is in the centres of these appearances 

 that the frustule, or a portion of it, is in optical contact 

 with the cover glass. Having located this position, if an 

 oil immersion objective be used, immensely superior deii- 

 nition will be found to be obtained at this point of optical 

 contact than can be secured on other parts of the diatom 

 which may not be so close to the cover." 



Cleaning Oil-Imnrversion Objectives. 



Dr. Henri \'an Heurck calls attention to the advan- 

 tage of using saliva as a means of cleaning oil-immersion 

 lenses. He first cleanses the objective and slide with a 

 piece of old dry linen of fine texture, then moistens an 

 end of the linen with a little saliva, and gently rubs the 

 objective front with it, using a magnifier to see if the 



cleaning is perfect. Owing to the slightly alkaline nature 

 of the saliva the cleaning is perfect, and practically instan- 

 taneous; and Dr. \'an Heurck says he has used this 

 method since 1878, and has never found it to fail, whilst 

 it keeps the front of his objcctixes as clear as when new. 



Popular Microscopical Lectures. 



I have received the annual list of lectures proposed by 

 the Extension Section of the Manchester Microscopical 

 Society for the ensuing winter. The scheme is so admir- 

 able and so well arranged that it deserves more than a 

 mere reference, lirielly, some 54 difl'erent lectures, selected 

 from the infinite variety of subjects dealt with by the micro- 

 scope and illustrated mostly by lantern slides, are arranged 

 to be given by some 20 members of the foregoing Society. 

 They are given to outside associations of all kinds who 

 make the necessary application, and, except in cases 

 where such associations are supported out of public funds 

 or are commercial speculations, are given free of charge 

 other than the reimbursement of actual out-of-pocket 

 expenses. The result is the bringing of scientific know- 

 ledge and information before those who would be unable 

 to pay large fees to professional lecturers, and the exten- 

 sion of the knowledge of microscopy and natural history. 

 Nowadays the microscope, whilst becoming daily more 

 and more necessary to the professional, finds many com- 

 petitors for favour with the amateur, and lectures of the 

 kind arranged by the Manchester Microscopical Society 

 should bring home to many the fascination of the micro- 

 scope as a recreati\e as well as educational instrument. 

 It would be well if the Quekett Club could see its way to 

 adopt a similar scheme ; in so large a district as is em- 

 braced by the Metropolis there should be no lack of 

 applicants for the services of its lecturers, and the result 

 could not fail to be of benefit to microscopy, and, inci- 

 dentally, to the Club itself. 



Notes and Queries. 



Wm. Watts, Bristol. 



Total length, -055 to '06 mm. Head, '0045 mm. long, 

 •0025 mm. broad, •0015 mm. thick. Middle piece or body, 

 •006 mm. long and less than '001 mm. in diameter. Tail, 

 •045 mm. long and finer than the middle piece. 



J. M. Dunbar, East Griquaiand. 



I am sorry that I do not know of any good book dealing 

 with the microscopical examination of adulterated foods. 

 Such an examination is really a matter for the specialist, and 

 the microscopical examination would be only part of a wider 

 examination, chemical and otherwise. If you can read 

 German, perhaps Dr. Herman Hager's " Das Mikroskop und 

 seine Anweadung," published in Berlin, might serve as an in- 

 troduction. It could be ohtamed from Williams and Norgate, 

 Covent Garden, London, for about seven shillings and postage. 

 I wonder if any of my readers know of any other book ? 

 Microscopical Material. 



Mr. W. S. Kogers has kindly sent me for distribution a 

 quantity of capsules of Funaria bygromdrica, the peristomes 

 of which make very beautiful dry mounts, and are curious 

 owing to the changes they undergo when wet and dry respec- 

 tively. I shall be glad to send a few of these to any reader 

 enclosing a stamped addressed envelope together with the 

 coupon appearing in another part of this issue. In case the 

 lids have not been shed they may be removed with a fine 

 needle, but great care is requisite. 



' Communiciitions and enquiries on Microscopical matters arc invited, 

 and ikould lie addressed to F. Shil!ini;tun Scales, "Jersey, "St. 

 Barnabas Road, Cambridge.] 



