56 



SCIENCE- G OS SIP. 



world are likely to be found the characteristic 

 rotifers of stagnant water, with little regard to the 

 country ; in clear lake-water, everywhere, the 

 characteristic limnetic Eotifera may be obtained; 

 in sphagnum swamps the Sphagnum or moss Eoti- 

 fera. Variation in the rotifer fauna of different 

 countries is probably due to variation in the con- 

 ditions of existence in the waters of those countries, 

 not to any difficulty in passing from one region to 

 another. In the introduction the author gives a 

 word of warning against the naming of species by 

 those persons who, through want of experience or 

 knowledge of what is known, arc not in a position 

 to differentiate new forms. Such work he describes 

 as a positive injury to science and a nuisance to 

 all careful scientific students. It is to be hoped 

 that everyone wishing to describe a new species of' 

 rotifer will learn by heart and inwardly digest this 

 sentence. In the very next paragraph the journal 

 refers to a contribution on this subject to the 

 " Trans. New Zealand Inst,," by Mr. F.W. Hilgendorf . 

 which comes under the above strictures. The 

 author succeeded in finding sixteen species of 

 rotifers, twelve of which he describes as new. 

 Half of these can at once be recognised as old 

 acquaintances, and the other half are of no value, 

 and scarcely to be identified as rotifers. The figures 

 of the four plates, remarks the writer of the notice, 

 bear about the same relation to rotifers as the 

 wooden blocks in a child's Noah's Ark do to the 

 animals they pretend to represent. 



Sections of Brazilian Lianas. — Further in- 

 formation (see S.-G., n.s., vol. vii., p. 372) upon this 

 subject is to be found in Professor Balfour's 

 "Manual of Botany" (1849). This work, though 

 rather old, gives some interesting particulars of 

 these and other stems under the heading of 

 " Anomalies in the Structure of the Exogenous 

 Stem." A figure is given (fig. 106) which closely 

 resembles fig. 3 on p. 374 of vol. vii. of Science- 

 Gossip, and in connection with this Balfour says : 

 " Some have supposed that the lateral masses are 

 undeveloped branches united together under the 

 bark ; but Treviranus considers them as connected 

 with the formation of leaves, and as depending on 

 a peculiar tendency of the vascular bundles to be 

 developed independently of each other round 

 several centres." The name of the plant from 

 which this section was taken is Paullinia pinnata, 

 one of the Sapindaceae of Brazil. Another figure 

 is given of a stem (Bignonia capriolata) resembling 

 fig. 2, p. 373, vol. vii. of Science-Gossip, but the 

 radiating plates are only four in number. These 

 are " probably formed by introversion, or growing 

 inwards of the liber. In some Guayaquil Bignonias, 

 Gaudichaud perceived, first, four of these plates, 

 next eight, then sixteen, and finally thirty-two." — 

 Herbeit Owen, 3 Nelson Street, Hertford. 



ANSWEES TO CORRESPONDENTS. 



G. B. (Coleraine). — There are several ways of 

 accounting for your difficulty. You are using too 

 strong a light, as there is no necessity for the bull's- 

 eye. Use the edge of the lamp-flame and focus it 

 carefully in the centre of the field, first centering 

 your condenser. Then stop down the iris dia- 

 phragm gently, as much as it will bear without 

 blurring or coarsening the image. Few achromatic 

 objectives will stand more than a | or | cone of 

 illumination, and many objects require consider- 

 ably less. Finally adjust your tube-length care- 



fully. It is not sufficient on critical images to go 

 by the nominal tube-length for which objectives 

 are corrected; further corrections must be made 

 for varying cover-glass thicknesses. If this does 

 not do away with most of the haze of which you 

 complain you must use a light filter, such as Gif- 

 ford's malachite green screen, or even blue glass. 

 Your objectives must be free from dust. All the 

 lenses mentioned have a fair ratio of aperture to 

 power, and will therefore have only moderate 

 " penetration." If still unsuccessful write to me 

 again. 



[For further articles in this number on Micro- 

 scopic subjects, see pp. 36, 37, and 44.] 



MEETINGS OF MICEOSCOPICAL SOCIETIES 



Quekett Microscopical Club, July 13th, Wimble- 

 don Common, from Putney. 



EXTRACTS FROM POSTAL MICROSCOPICAL 

 SOCIETY'S NOTEBOOES. 



[Beyond necessary editorial revision these ex- 

 tracts are printed as written by the various 

 members. — Ed. Microscopy, S.-G.] 



Scales of Fishes. — The scales of fishes are 

 objects of interest to the. geologist and the zoologist 

 as much as to the microscopist, and are therefore 

 at all times an interesting study. They are im- 

 portant features in classification, throwing light 

 on the conditions of the waters inhabited by their 

 possessors, and so contribute not only to the under- 

 standing of the conditions and life of the present 

 seas, but add their quota to the sum of our know- 

 ledge of the former conditions of life upon the 

 earth. The scales of fishes, unlike the scales of 

 most reptiles, are not epidermal appendages — i.e. 

 they do not grow upon the skin, like hairs, nails, 

 or hoofs, but are produced within the substance of 

 the skin, and are covered throughout their extent 

 with a layer of it. A cursory glance will show 

 that the scales figured herewith are of two kinds, 

 those having a comb-like appearance at one end. 

 and others without this characteristic. The former 

 are known as " ctenoid," and the latter as " cycloid." 

 In the ctenoid the comb-like end is the free end, 

 the scolloped part being imbedded in the skin. 

 The scales are so arranged in relation to each other 

 that the water glides from the edge of the one on 

 to the middle of the next. The scales overlap in 

 the direction from head to tail of the fish. Two 

 objects are attained. - The fish swims with the 

 least possible amount of friction, and the 

 underlying skin is shielded from the constant 

 maceration to which it would be subject if 

 the water were perpetually soaking between. 

 Unlike the armour-plated " placoid " and sheeny- 

 coated " ganoid " fishes of the geologic seas, 

 which still have their representatives in our 

 modern waters, the scales here shown are delicate 

 and flexible. "Ctenoid" and " cycloid "' differ in 

 appearance'; but whether comb-like or rounded the 

 structure is very much the same. An examination 

 will show a number of consecutive lines which 

 correspond approximately to the shape of the 

 scale. A little careful focussing reveals also that 

 the scale, however thin, is thicker at the centre 

 and thin towards the edges. In some scales the 

 concentric lines are continuous across the furrows 

 formed by the deep radiating lines of the upper half. 

 In the flounder and perch they do not meet, but 

 are broken by a line of transparent matter which 



