Al'GUST, 1911. 



KNOWLEDGE. 



321 



panacea. Gcodia gigas. Spoiigilla laciisfris. and the entire 

 sponge (young) of Lcitcosolcnia hotryoidcs : this last slide 

 shows the budding of a sponge. The section of Granfia 

 coinpycssa exhibits the collar-cells [choanocytcs) ; the fresh- 

 water sponge (S. lacitstris) shows the "gemmules," vide 

 page 59. The three plates referred to above illustrate Mr. 

 Abraham Flatters' paper, which is devoted to the preparation 

 of slides illustrating the histologv of the wheat plant. 



THE DWARF PLANKTON.— In connection with the 

 short report in " Knowledge" (June, page 236) of my paper 

 on '■ The Use of the Centrifuge in Pond-Life Work," read 

 before the Quekett Microscopical Club in April last, I should 

 like to call attention to a little pamphlet recently published 

 by Professor H. Lohmann. of Kiel, entitled, " L'eber das 

 N'annoplankton und die zentrifugierung kleinster Wasserproben 

 y.nv Gewinnung desselben in lebendem zustande " iW. 

 Klinkhardt, Leipzig, M. 1'50). The term Nannoplankton 

 (I'dj'i'os = dwarf) has been coined by Lohmann for the 

 e.xtremely minute forms of life existing in water, the 

 forms, in fact, which pass easily through the meshes 

 of the finest silk gauze, and his paper is in the main a 

 summary of the additional knowledge which has been gained 

 about these organisms by the use of the centrifuge. The 

 application of this instrument to the special purpose of 

 collecting these very minute organisms is due to Lohmann, 

 who was led to the conclusion that something supplemental to 

 nets, or even filter papers was wanted as a means of collecting 

 the smaller constituents of the plankton, by observing 

 the rich and varied accumulations of tiny protists 

 obtained by the extraordinarily line filtering apparatus 

 of some marine animals such as the Appendicularia. 

 The method of centrifuging water in order to con- 

 centrate the contained " Nannoplankton " is undoubtedly 

 a very powerful new means of research, and it can no longer 

 be ignored by those interested in the life of our seas and 

 fresh-waters. Very small quantities of water are sufficient as 

 a rule (1 often work with tubes holding onl\- one-and-a-half 

 cubic centimetres! and the bulk of the forms present are 

 deposited in one or two minutes if the centrifuge be run at a 

 fairly high speed, say two thousand to six thousand revolutions 

 per minute. Practically no damage is done to the organisms 

 during the process of centrifuging, and if examined immediately 

 after, they will be found to be alive, so that even the most 

 sensitive and fragile of the naked forms can be recognised. 

 This, it need hardly be pointed out, is an utter impossibility 

 with collections made by any straining method yet invented. 

 The Nannoplankton is composed of bacteria, protophytes 

 (schizophyceae, desmids, diatoms, chlorophyceae, phyto- 

 flagellates), and protozoa (rhizopods and zooflagellates). 

 the bulk being usually formed by the phytotlagellates. 

 The comparative volume of the Nannoplankton is small, 

 but as Lohmann points out this does not prove that it is 

 of no importance in the economy of the sea and fresh-waters. 

 " The degree of importance in this respect depends essentially 

 on the rapidity of the multiplication and the duration of life- 

 time, as well as on the nutritive character of the organisms 

 themselves. In this latter direction the Nannoplankton 

 surpasses perhaps all the other Plankton and in the former 

 respect it equals the other Protists at least. Should one wish 

 to estimate the importance of the three chief groups of 

 Plankton only according to their average life-time, one must 

 place on a par one volume of Bacteria to about six volumes of 

 Protists and to about three hundred volumes of Metazoa." 

 For those who cannot read German there is an English 

 summary appended to the paper, which is also accompanied 

 by five plates of Nannoplankton organisms, drawn to scale, in 

 frames representing a single opening in the silk gauze used for 

 the finest Plankton nets. 



D. J. ScouRFiELD, F.Z.S., F.R.M.S. 



QUEKETT MICROSCOPICAL CLUB.— June 27th. 1911, 

 Mr. C. F. Rousselet, F.R.M.S., Vice-President, in the chair. 

 Mr. J. W. Ogilvy exhibited for Messrs. Leitz a recent 

 invention, on the principle of the dark-ground illuminator, for 

 rendering visible the particles in smoke and gases, and in 



liquids. Messrs. Watson exhibited a series of seven prepara- 

 tions, illustrating the development of the chick. The stages 

 were twenty-four, thirty-two. forty, forty-eight, sixty, seventy- 

 two and ninety-six hours of incubation. 



A paper by Dr. E. Penard. on " Some Rhizopods from 

 Sierra Leone " was read by Mr. Earland. The material 

 examined was collected from a " slow, large river, containing 

 weeds." Fourteen species had been found, of which three 

 were new. and four at least might be considered as special 

 forms or varieties. The genera represented were : — 

 Ceiitropyxis, two species; Difflugia. five species (two new) ; 

 Englypha. two species ; Lcsqucrcntia, three species (one 

 newl ; and Pontigtilatia, two species. The author expressed 

 his indebtedness to Mr. G. H. Wailes for the material received 

 and hoped that time and opportunity would be found for 

 further investigations. 



Mr. T. A. O'Donohoe read a note on " Dimorphism in the 

 Spermatozoa of the Flea and the Blow Fly." Only about 

 70% of the specimens examined had the two forms noted, the 

 minority having only the smaller form. The spermatozoa of 

 the flea are very large compared with those of man, whose 

 spermatozoa have an average length of about • 06 millimetres. 

 In the flea the larger form is 0-7 to 0-45 millimetres long, 

 and the smaller form about half these lengths. Both are 

 similar in structure and stain well with dilute carbol-fuchsin 

 or gentian-violet. The two forms found in the Blow Fly are 

 smaller than those of the flea. They do not differ much from 

 each other in length, but one is very much thicker than the 

 other. Photomicrographs of the specimens described were 

 projected on the screen. 



A paper by Mr. E. M. Nelson, F.R.M.S., on " Normal and 

 Abnormal Vision in Microscopic work," was read by the 

 Assistant Honorary Secretary. The experiments described 

 showed the effects of long and short sight upon the magnifying 

 power of the microscope. The differences are most marked 

 with low powers. The author's sight being presbyopic, 

 biconvex glasses are required to make it normal. When 

 ineasm'ing the pow-er of a microscope by means of a camera 

 lucida, it is therefore necessary to use spectacles, otherwise, 

 while the image of the micrometer in the microscope is sharp, 

 that of the exterior scale, at ten inches distance, would be 

 invisible to him. Experiment 1. — The power of a '" loup " 

 (focus about 1-6 inch) was measured, the spectacle lens being 

 below the camera. The power was 6. Experiment 2. — As 

 before, but with the spectacle lens above the camera ; the 

 power was 7. Experiment 3. — .A double pair of spectacles of 

 equal power were used ; the presbyopic eye was therefore made 

 myopic. A conca\e lens, which precisely neutralised one of 

 the spectacles lenses, was placed below the camera. The 

 ■' loup " now ga\'e power 8. Experiment 2 shows the power' 

 of the " loup " with normal sight. The experiments on being 

 repeated with a compound microscope giving six diameters 

 showed similar results. It is generally understood that 

 persons with short sight have wonderful pow-ers of seeing 

 minute objects, but few realize that anyone with three 

 dioptres of myopia can with a six-power " loup " see as much 

 as one having three dioptres of presbyopia with an eight- 

 power " loup." Further experiments were also described. 



ROYAL MICROSCOPICAL SOCIETY.- June 2Sth— Mr. 

 H. L. Plimmer, F.R.S.. President, in the chair. — Mr. Strachan : 

 The structure of scales from Thcnuobia doinestica Packard. 

 The author showed that the longitudinal striae which appeared 

 to project at the free margin of the scale were in reality the 

 walls of a set of longitudinal tubes, and when pressure was 

 applied to the scales the tubes might be made to collapse and 

 disappear, and in some instances, when heat was applied, both 

 fluid and air bubbles were observed to traverse the tubes. 

 These tubes were on the convex side of the scales. Radial 

 striae also crossed the longitudinal striae at various angles, 

 and the author illustrated his paper by an ingenious model 

 composed of two sets of parallel thin glass tubes in close 

 contact, almost filled with fluid and sealed at the ends, one set 

 containing oil of turpentine, the other ethyl alcohol. One set 

 of tubes was fixed ; the other set, placed in contact with them, 

 could be rotated over a considerable angle. By illuminating 



