May. loi: 



KNOW LI-.DGi:. 



193 



nor any appearance of a tendency in the filaments to emerge 

 on the surface of the leaf, as would be expected as a 

 preliminary to the process. The family — Phyllosiphonaceae — 

 is mostly tropical and several 

 species are known as occurring 

 on the leaves of various hosts, 

 but the one under considera- 

 tion is found only in the North 

 of Italy, and the South of 

 France. Figure 225 .A is a 

 portion of leaf, slightly magni- 

 fied, showing the course of 

 the filaments, in H some are 

 dissected out, giving their •: 

 general appearance ; at the 

 bottom is a piece of the 

 partially disorganized lower 

 cuticle with the parasite 

 spreading from the remains of 

 the leaf cells, X about fifty. 



].\s. Hlkton. 



KOV.\L MICROSCOPI- 

 CAL SOCIETY. — March 

 _'Oth, 1912. Edward Heron- A. 

 .Allen, Esq.. F.L.S., Vice- 

 President, in the chair. — 

 Mr. C. F. Rousselet described a 

 which had been presented by 

 Lieberkiihn devised this form of 

 it was intended principally for 



which wore illimiinated by a silver concave speculuin in 

 the cOTitre of which was mounted a bi-convex lens. The 

 combination of a lens and reflector was invented by Descartes 

 in 1637, but it remained for Lieberkiihn, 100 years later, to 

 apply it in a convenient and serviceable form. The reflector 

 is known as a " Lieberkiihn " and is used at the present day. 

 Mr. Kousselet also described two old microscopes lent for 

 exhibition by Mr. T. H. Court. The first, a small portable 

 simple microscope, signed I. Cuff, was probably made about 

 1750. The pillar is inclinable and is mounted excentrically 

 upon a thin oval brass plate upon which it can be rotated 

 to give stability to the instrument in difterent positions. 

 It has a fine adjustment of the John Marshall type to the lens- 

 holder. There is a concave mirror, 

 which with the lens-holder, stage and 

 oval foot are hinged so that they can 

 be folded up. It seems probable that 

 this instrument may have been the 

 parent model of Ellis's .-Vquatic Micro- 

 scope. The second microscope was 

 by Watkiiis and Smith, who were in 

 partnership from 1755 to 1775, which 

 circumstance fixes the date of the 

 instrument. The general features 

 are similar to those of a microscope 

 made entirely of silver by Francois 

 Watkins that was exhibited at a 

 Meeting of the Society in Xovember, 



1907, the date of which was about 1754. Watkins at this 

 date was '■ Optician to their Royal Highnesses Prince and 

 Princess of Wales, at Sir Isaac Newton's Head, Charing 

 Cross." This latter microscope was wanting in rigidity, but 

 the model now exhibited was more substantially made and 

 was free from vibration. The fine-adjustment in the silver 

 microscope was absent and a strong rack-and-pinion coarse 

 adjustment applied to the stage was substituted. There are 

 se\en powers mounted on a disc between two brass plates. 

 The instrument is inclinable and can be used as a simple or 

 with a body and eye-piece, as a compound microscope. The 

 mirror is double, plane and concave. 



Mr. Conrad Beck exhibited the " Focostat Lens," described 

 below. 



Mr. E. J. Sheppard exhibited two slides. The first was a 

 vertical section through the four upper incisors of a kitten 

 about six days before birth, the section passed through nearly 



Portion of a leaf infected with Pliyllosiplioii. magnified 

 B. Filaments dissected out X 50 approximately. 



Lieberkiihn Microscope 



Mr. .\lpheus Smith. 



nicroscope about 17JS ; 



viewing opaque objects 



Figure 226. 

 Hiscott's " Focostat Lens. 



an equal plane 'in each tooth. .Mr. Sheppard also described 

 the method of staining adopted. The second slide showed 

 the second maturation division in the ovum of a mouse 

 prior to its leaving the ovary. 

 : Mr. C. F. Rousselet then 



described four Rotifera from 

 the Devil's Lake, a large 

 brackish-water lake in North 

 Dakota, the point of interest 

 being that all four species lived 

 in brackish water only. One, 

 I'cdtilioii fc'imictiiii, was first 

 found in Finland, another was 

 a new species, liracltioniis 

 spiitiosiis, the third Britchi- 

 oiiiis sat aniens Rousselet. 

 known only from this locality, 

 and the fourth was4s/)/<7«c/iH« 

 silvcstrii Doday, E. P., show- 

 ing dimorphism in the female. 

 Mr. F. Enock gave a lecture 

 on " I'airy Flies and their 

 Hosts." His interest in these 

 minute flies (Myniaridae) was 

 excited by seeing one that was 

 exhibited by the late Frederick 

 Fitch at a Conversazione given 

 by the Society in 1875 or 1876. At that time the only 

 illustration known was that of a very minute insect drawn in 

 1797 by Dr. Grey, of the Royal Society, and published in the 

 Linnean Society's Transactions. Up to four years ago Mr. 

 Enock had worked on the subject alone. He was then joined 

 by Mr. Chas. Waterhouse, of the Natural History Museum. 

 The interesting fact was that the eggs ot the Myniaridae are 

 deposited in the eggs of destructive flies. The lecture was 

 illustrated by many beautiful slides prepared by Mr. Enock, 

 including a series of photomicrographs illustrating the life 

 histor>' of the fly from the time its egg was deposited in its host. 



THE NEW FOCOSTAT LENS.— The Focostat lens is 

 the invention of Mr. T. H. Hiscott, a member of the Royal 

 Microscopical Society, who devised it for his own use in the 

 field. Those who know the difficulty of di-ssecting a flower 

 under a high power lens will realise the great ad\^antage of 

 this contrivance. Even if the flower 

 can be held by some means while the 

 lens occupies one hand and a needle 

 or scalpel the other, the slightest 

 motion puts the lens out of focus. 



In the invention under consideration 

 (see Figure 226) the lens is carried on 

 the needle itself. It is focused once 

 for all on the point of the instrument 

 and follows every movement. The 

 lens has a magnifying power of about 

 seven diameters. It can be slid along 

 the handle of the knife or needle and 

 adjusted to the angle at which the 

 observer is in the habit of holding his 

 hand. It has proved to be most useful in zoological and 

 botanical dissections and for fine drawings with a mapping 

 pen. while many other uses will suggest themselves. 



Messrs. R. & J. Beck, of 68, Cornhill, are putting the 

 Focostat lens on the market together with dissecting knives 

 and needles, mapping pens, and retouching pencils with 

 circular handles on which the Focostat is interchangeable. 



Mr. Hiscott is greatly to be congratulated upon his 

 extremely useful invention. 



THE PSEUDOPODIA OF D I ATOM S. — Several 

 observers, noticeably Mr. Grenfell and Professor Van 

 Heurck. have discovered the appearance of projections from 

 diatoms particularly in the genus Coscinodisciis, but it has 

 been argued successfully up to the present that they are not 

 parts of the diatom itself and are possibly parasites. At the 

 meeting of the Royal Microscopical Society, held on March 



