76 



KNOWLEDGE. 



February, 1910. 



blepharoplasts now travel to opposite sides of the nucleus, and 

 take on the function of centrosonies. The nucleus breaks np 

 into chromosomes, its membrane disappears, a mitotic spindle 

 is formed in the nsual way, with t!ie two centrosomes at its 

 poles. The two new flagella then at once begin to grow out 

 from the two centrosomes, outside the original collar and 

 before the equatorial plate is divided. The mitosis is com- 

 pleted, and as the cell-body divides, the original collar breaks 

 down and disappears. The centrosomes become the blepharo- 

 plasts of the two dausjl'ter-cells, the flagella continue to gnjw 

 out from them, the n^-w collars grow up round the new flagella, 

 the daughter-nuclei return to the bases of the cells, and the 

 two daughter-cells resume the structure and appearance of 

 the ordinary resting collar-cell. It is thus seen that the 

 blepharoplast-centrosome is a permanent cell-organ which 

 divides with the cell, while the collar and flagellum are formed 

 afresh at each cell-division. 



ORNITHOLOGY. 



By Hugh Boyd Watt, M.B.O.U. 



THE BOYD ALE.XANDER COLLECTIONS.— The very 

 fine and extensive collections of bird-skins made by the late 

 Lieutenant Boyd Alexander, in the course of his scientific 

 journeys in Africa, are to go to enrich the national collections 

 at the Natural History Museum, South Kensington. Lieutenant 

 Alexander, who, it will be remembered, was killed in the 

 course of explorations in Africa last year, died intestate, 

 but, in accordance with his wish, the Museum above- 

 named is to have his collections. These are housed at present 

 in a private museum, which was specially built for them 

 at Wilsley. The collections are from wide areas in Central 

 Africa, visited since 1897, including the Cape Verde Islands. 

 Zambesi River, Kumassi, Fernando Po, and the great regions 

 travelled through from 1904 to 1907, described in Lieutenant 

 .iXlexander's book, entitled "From the Niger to the Nile," also 

 from the islands of San Thome, Principe and Annabon, and 

 Cameroon. Lieutenant Alexander obtained many species new to 

 ornithology and science, and described (and in some cases figured ) 

 them in the pages of the Ibis, and of theBiillctiii of the British 

 Ornithologists' Club. In a comparatively short life, devotion 

 to his favourite pursuit yielded a rich harvest, and the memory 

 of this intrepid traveller and ornithologist will be further 

 perpetuated by this splendid gift to the nation and to science. 



MIGRATION. — It is good news to ornithologists that 

 Mr. William Eagle Clarke, of the Royal Scottish Museum, 

 Edinburgh, is .ibout to publish a work dealing with the 

 study of bird-migration in the British Isles. It is not too 

 much to say that, despite much writing (or, perhaps, because 

 of it) knowledge lingers here, still in the obscurity of 

 conjectures and surmises, and the time is ripe to attempt an 

 advance on a genuine scientific basis. From no one is new 

 and clear light more likely to come than from Mr. Clarke, who 

 has devoted many years, dating back to the days of the 

 Migration Connnittee of the British Association, to the stud\- 

 and accumulation of facts and observations. Besides having 

 at his command the long series of reports made year after 

 year by many observers and recorders throughout the country, 

 Mr. Clarke has, within recent years, spent lengthened periods 

 at the migration seasons in outlying localities from the 

 Eddystone Rock in the south to the remote islands in 

 the north, on the fly-lines, or routes of migrants. Readers of 

 his preliminary reports and notices know that he has gathered 

 abundant and rich results. A mere enumeration of species 

 does not in itself throw light on migration problems, still it 

 is notable that the small Fair Isle (between Orkney and 

 Shetland), has yielded records of no less than one hundred 

 and ninety eight species of bird visitors, including man\' 

 which experienced ornithologists have never seen in Britain. 

 For instance, the year 1910 gave three species new to the 

 faunaof Scotland, viz., the Hoary Redpoll (Acanthis exilipcs). 

 Holboll's Redpoll {A. linaria holboclli) — a second example 

 occurred on the Isle of May, October 2Jrd — and the 

 Yellowshank (Totanus flavipes). (Ann. Scot. Nat. Hist.. 

 January, 1911, page .S3). 



A NEW BRITISH BIRD.— Amongst the birds observed 

 and procured by Mr. Wm. Eagle Clarke at St. Kilda — the 

 furthest west and most remote of the British Isles — last autunm 

 (1910), was the American Pipit iAntlius pcnsylvanicus). new 

 to the British fauna, and the Marsh Warbler (Acroccphalus 

 pahistris), new to Scotland. (.4;;//. Sco^. Wat. Hist.. JSLnu3.iy 

 1911, page 52). The rarity of the Pipit named is so great that 

 the only mention of it to be found in Dresser's " Manual of 

 Palaeartic Birds" (1902) is a statement that it so nearly 

 resembles A. spipoh'tta as to have been included, in error, 

 as a European bird. 



A PROPOSED CENSUS OF TUK COMMON HERON 

 (Ardea cinerea). — Such a bird as this, large in size and 

 sedentary in habits, affords the possibility of some success 

 attending an attempt to number the individuals in a limited 

 area. A proposal is being mooted to undertake this enumera- 

 tion in Scotland, where the location of the Heronries, which 

 are widely distributed over the mainland, is pretty accurately 

 known at present. This wide distribution may, however, prove 

 a serious difficulty in the attainment of accuracy or complete- 

 ness of returns. The numbers of several species of British 

 birds are known, but these are mostly inhabitants of restricted 

 areas or individually scarce, or where the species may be called 

 common, e.g.. the Gannet, its occurrence is concentrated (at 

 any rate at the breeding season) at a few well-known stations. 



PHOTOGRAPHY. 



By C. E. Kenneth Mees, D.Sc. 



THE MICROSCOPIC STUDY OF DRY PLATES.— 

 Dr. W. Scheffer, of the University of Berlin, in his lecture at 

 the Royal Photographic Society on December 20th, described 

 the investig.ations which he has made on the effect of exposure 

 and development upon the individual grains of a gelatino- 

 bromide emulsion. He has designed for his work a very 

 complete experimental equipment, and his photographs are 

 all taken at a magnification of two thousand diameters, 

 much higher than has been used by previous workers in the 

 subject. Photographs taken of grains during the process of 

 development show that the grains are of two kinds, which 

 Dr. Scheffer distinguishes as " original grains " and " nourishing 

 grains." The original grains have filaments projected from 

 them, either during exposure or at the commencement of 

 development, and Dr. Scheffer concludes, from his later 

 observations, that grains showing these filaments remain 

 unaltered during the progress of development, and become 

 covered by the metallic silver which is deposited upon them, 

 this metallic silver being derived from the solution of the 

 '■ nourishing grains," which disappear during development. 

 When a plate is under-exposed there are few original grains 

 present, and with o\er-exposure many original grains and few 

 nourishing grains, a fact to which Dr. Scheft'er ascribes " the 

 lack of density produced by over-exposure." This seems to 

 require re-consideration, because ordinary over-exposure does 

 not produce lack of density; the thinness which most amateurs 

 assign to over-exposure is due to under-development ; if an 

 over-exposed plate be developed for the normal time, it will be 

 extremely dense all over. Possibly, however, Dr. Scheffer 

 intended the reversal period by "over-exposure." The con- 

 nection of these observations with the known facts as to the 

 chemical dynamics of development will require a great deal of 

 work. It is not at all obvious, for instance, that a steady growth 

 of original grains and diminution of nourishing grains would 

 be in harmony with Hurler's " Law of the Constancy of 

 Density Ratios," which is the photographic equivalent of the 

 mass-law. 



Moreover, the statement that there are silver bromide grains 

 in the film of a plate which are unaltered in development and 

 which can survive fixation, should be capable of confirmation 

 by chemical experiments on plates in the mass, and the amount 

 of such grains should be readily ascertainable if developed 

 and fixed plates are treated with a solvent of silver which is 

 incapable of affecting silver bromide. Dr. Scheffer showed an 

 experiment in which this was done, but this would require con- 

 firmation by quantitative megisurement on masses of developed 



