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SCIENCE-GOSSIP. 



Freshwater Mites and Corixa.— On the 

 5th of May, 1898, I made an excursion to collect 

 freshwater mites, and the day following, I found 

 in the water brought home, Covixa geoffroyi, with a 

 few of the larvae of some freshwater mites. These 

 were tolerably advanced in growth, attached to 

 the oar of the creature. They reminded me of 

 the so-called Aclysia dytisci, figured and described 

 by Mr. Ball in " The Journal of Microscopy and 

 Natural Science " for October, 1885. I placed the 

 Covixa in a small specimen jar, with pond water 

 and a little weed and mud, and covered' it over with 

 a loosely-fitting piece of glass ; previous experience 

 having taught me that Corixa usually tries to 

 escape. I had the satisfaction of finding that all 

 went well, and on the 10th of May I noticed that 

 one of the attached parasite skins had become 

 lighter in colour, and flaccid, the contents having 

 escaped. On further search I found a specimen 

 of Hydrachna globosa De Geer swimming freely in 

 the water. I had, of course, previously taken care 

 that no water- mites were in the water of the jar. 

 Hydrachna globosa is distinguished from other 

 species of Hydrachna by two thickened portions of 

 skin, one below each double eye. These are to be 

 seen when the creature is alive, and are rather 

 darker in colour than the rest of the skin ; but 

 after mounting in balsam, they become too trans- 

 parent to be very' well made out. On the 30th of 

 May I found another Hydrachna globosa at liberty. 

 I do not know exactly when it became free, as I 

 did not examine the jar very frequently after the 

 finding of the first Hydrachna. I have succeeded 

 in obtaining from this one set of observations 

 three useful and interesting slides : oar of Corixa 

 with parasite attached ; another being part of 

 Corixa with the empty skin and head-part of larva 

 attached after the escape of the nymph ; the third 

 being the escaped nymph. I trust that the publi- 

 cation of these observations may induce other 

 observers of pond life to follow my example during 

 the coming season, and publish the results in 

 Science-Gossip. A very little trouble will insure 

 accuracy, and the results may be valuable. Should 

 there be any difficulty in making out the specific 

 name of the mite produced, I shall be glad to 

 endeavour to identify the specimen, if sent to me in 

 a living state in a little water ; and I have no doubt 

 that Mr. Soar would be glad to do the same. In 

 "The Illustrated Annual of- Microscopy," 1898, I 

 find a plate by Mr. Soar, giving a good drawing of 

 leg of Corixa, with two parasites attached ; also 

 outline figures of Hydrachna globosa, Hydrachna 

 crucnta, etc. — C. F. George, Kirton-in-Lindsey ; January 

 14th, 1899. 



The Sheffield Microscopical Society. — 

 The microscope in Medicine, and particularly in 

 Bacteriology finds an enthusiastic advocate in 

 Dr. Porter. In the course of his inaugural 

 address to the Sheffield Society he laid great stress 

 upon the necessity of forming local societies for 

 microscopical research, and the benefit that 

 members derived from them. One of these 

 advantages was that it brought on common ground 

 those who were interested in microscopical work 

 of every kind — biological, chemical, botanical, 

 mineralogical or medical. It facilitated the special 

 work of each, and at the same time made those 

 who were engaged in one branch of science 

 acquainted with what other workers were doing, 

 the use of the microscope being the point of 

 contact. He referred to the immense possibilities 

 of the application of the microscope to the science 

 of bacteriology. 



Fossil Radiolaria. — For some years past Dr. 

 Rust has been at work on the Radiolaria of the 

 Paleozoic, Jurassic and Cretaceous rocks. He has 

 now contributed to the current issue of " Paleonto- 

 graphica," vol. xlv., an important addition to our 

 knowledge concerning this group of organisms 

 by revising his earlier monographs on the Radio- 

 laria of the Secondary rocks, and thus furnishing 

 us with a trustworthy standard of reference as to 

 the character of the micro fauna of the beds in 

 the Tyrol, Bavaria and northern Italy. His 

 monograph is illustrated with some of the 

 hundreds of microscopical sections which he has 

 prepared of the nodules of silicious limestones 

 from Cittiglio. The microscopical examination 

 of these revealed no less than 212 new species. 



Saxtonixe Crystals. — Of the many forms of 

 crystals, there are few that surpass these for beauty 

 and variety of design. If the microscopist care- 

 fully follows these directions, he will invariably 

 succeed in producing a good slide. Make a cold 

 dilute solution (one or two per cent.) in chloroform, 

 drop on a cold slide, and heat rapidly over the 

 flame of a spirit-lamp. — Frederick Noad Clark, Pad- 

 dington Infirmary, Harrow Road, London, W. 



Progress in Micro-Photography.— Messrs. J. 

 E. Barnard and T. A. B. Carver recently explained 

 in " Nature " how 7 they have overcome the difficulty 

 experienced in micro-photography with high 

 powers and critical illumination owing to the 

 unequal intensity of the light emitted from the 

 surface of the incandescent limes, or the im- 

 possibility of controlling the electric arc so as to 

 maintain a constant position and condition of the 

 crater on the positive carbon. The latter "difficulty 

 they have overcome by having a simple form of 

 hand-feed apparatus, with a pin-hole camera 

 attached, through which an image of the carbon- 

 points is projected on to a ground- glass screen. 

 With such a form of arc-lamps absolute " centra- 

 tion" of the light can be secured and maintained, 

 without reference to the microscope, after the 

 necessary position of the image of the arc on 

 the screen of the pin-hole camera has been once 

 obtained. 



Micro-Photography. — Where can I get in- 

 structions as to the best way of photographing 

 whole insects mounted in balsam which are too 

 large to be contained in the field of a microscope 

 with low powers, such as a two-inch objective and 

 B eyepiece? — E. J. Wheeler, Alnwick Castle Estati 

 Office, Northumberland. 



[We have invited Mr. Frederick Noad Clark, a 

 most successful micro-photographer, to reply to 

 this query. He says: — "To photograph insects 

 and other objects (mounted transparent in 

 balsam, etc.) which are too large to be contained 

 in the field of a microscope with low powers, e.g., 

 a two-inch, I should recommend the use of a three- 

 or four-inch objective. But if the object is too 

 large for these, then use an ordinary photographic 

 lens of wide angle in place of the micro-objective, 

 and a camera having a long extension if necessary ; 

 or, better still, the new " Planar " lenses, by Ross, 

 are particularly adapted for this class of work, 

 using Nos. 1 to 8, according to the magnification 

 desired. If a micro-objective is used, an eyepiece 

 is unnecessary. Illumination is best effected by 

 interposing a piece of ground glass between the 

 bull's-eye condenser and the object." — Frederick 

 Noad Clark, Paddington Infirmary, Harroiv Road, 

 London, WJ] 



