Skptpmbbr. 1901.] 



KNOWLEDGE. 



213 



nourishing: situation develops into a female, that one of 

 the others then becomes what he calls " a definitive 

 male," the i-est having either to bide their time for 

 similar chances, or perhaps having to bo content with 

 the lot of Portia's unsuccessful suitors. One genus dis- 

 plavs a kind of inverted Monnonism, a solitary female 

 being privileged to have numeious mates strongly 

 attached to her. Messieurs C'auUery and Mesnil, 

 writing on //'/hci/uVi/.j hnlnui whidi is parasitic on 

 1 irripi>des, note that this is the only cnixtacean genus 

 vet known in which there are two oviducts on each 

 s:de,§ The ■ Notes on some crustacean paiasites of 

 fishes," by Mr. Thomas Scott, f.l.s.. ought not to be 

 neglected.il 



Of Dr, Birulas papers on Russian Malacostraca it 

 must suffice to say that though the crustaceans them- 

 selves ai-e not confined to the dominions of the Czar, 

 the discussion of them is, unfortunately for the mono- 

 glot Englishman, exclusively in Russian. I 



The spirited essays in which the eminent Dar,ish 

 zoologist. Dr. H. J. Hansen, has been appealing to his 

 countn'men to shake off political apathy, to cultivate a 

 stedfast friendship with Great Britain, and to set their 

 scientific household in order, would not come within the 

 scope of this chapter, but for the remarkable appendix 

 on " Rhizorhina, llcrpj-llobius, and Soren Jensen," 

 which the student of Entomostraca ought not to 

 overlook.* 



Here the account of current carcinology might 

 well have paused, had not the intention of stopping 

 been frustrated by the coincident aiTival of Major 

 Alcock s " Descriptive Catalogue of the Indian deep sea 

 Macrura and Anomala, t and of a pleasant work by the 

 same author, called " Zoological Gleanings from the 

 Royal Indian Marine survey ship ' Investigator,' "| In 

 contrast to the diminutive forms that nestle in corals, 

 the following passage from the " Gleanings '' shows us 

 land-crustaceans liolding their own in the struggle for 

 existence even against vertebrates: — "On Pitti Bank, 

 which is a little uninhabited sand-cay of one of the most 

 submerged of the Laccadive atolls, we found, at the 

 end of November, 1891. vast swarms of a large species 

 of sea-tern breeding. There were nestlings in every 

 stage, but no eggs. Both old and young birds were 

 quite free from fear, the old birds, almost alighting on 

 our shoulders as we landed, and the young birds, even 

 those with their first plumage complete, submitting to 

 capture without any resistance. Dreadful havoc had 

 been wrought among the young birds, chiefly by large 

 Coenobite hermit-crabs, with which the islet swamied, 

 but also to some extent by Ocijpoda ceratophlhalma. 

 The young broods were simply huddled together on the 

 ground, without any soi-t of nest, so that in the 

 absence of the parents they were at the mercy of the 

 crabs. Judging from the bones and sprouting quills that 

 covered the gi-ound, hiindreds of young birds must have 

 perished, and in several cases we saw recently killed 

 bodies lying under a living mound of voracious crabs." 



§ ' Bulletin Seientifiquft de la France et de la Belffique." Tol. 34, 

 I p. 316-362. plate? 17-18. (Paris, 19<n.) ' 



i Fisherr Board for Scotland. 18tli Annual Report, pp. 144-188, 

 plates 5-8. 190r). 



■" "Annuaire du Muj. Zoo', Acad. Imperiale des Sc-encea de St. 

 Petersbourg." 18!)9, 19<J0. 



• "Danmarks Stilling ogTiUtand." Af H. .1. Hansen, Dr. Phil. 

 Part 2, 216 pages. (Kjobenhavn, U)00.) 



+ Uo. 290 pages, 3 plates. (CaUutta, 1901.) 



X Eeprinted from the " Scientific- Memoir.^ Iiy Medical Ofllcers of 

 the Army, India." Part 12, pp. 3.5-76. 4to. (Simla, 1901.) 



Coridueted by 



I .Cep>ss. 



Thk Hf.mostat IX MicRo.siopY. — The microscopist who 

 has never seen a niicrcscope used in conjunction with a 

 heliostat has yot to learn the possibilities and advantages of such 

 a form of illumination. 



Residents in the British Isles have a substantial excuse for 

 not usini; the heliostat because of the uncertainty of s^ottinj,' 

 bright sunshine at the time of working ; still the intermittent 

 occasions on which it could be employed would well repay them 

 for their trouble. 



>[icr08Copists with leisure would find it nioi'C u.scful than 

 those who have few opportunities of workini,' in the day lime, 

 while those who live in foreign countries where continuous 

 sunshine can be depen<led upon are strongly recommended to 

 make trials of a heliostat. 



Its advantage is especially indicated in the illumination by 

 monochromatic light, for which purpose two right angle prisms 

 of dense glass with about 1 } inch face are necessary, with hulf 

 a rapid rectilinear lens to concentrate the light upon the prisms 

 and the remaining half placed to receive the spectrum as it 

 emerges from the |)risms. 



The microscope should be placed at some distance, say 1'2 to 

 1.') feet, from the prisms, the height of the heliostat being so 

 arranged that the beam from it shall fall upon the microscope 

 mirror. A strip of card should be set in front of the microscope 

 on a^ level with the mirror, and the room darkened as much as 

 possible, when it will be found, if the prisms are nicely adjusted, 

 that a brilliant image of the spectrum is projected. By slightly 

 moving the prisms or the microscope the exact wave length of 

 light that is desired for the work in hand can be selected, and 

 that wave length used for the examination or photography of 

 objects. The brilliance of illumination secured under these 

 circumstances is so great that light well into the violet end of 

 the spectrum can be satisfactorily utilised, and the resolving 

 power of objectives increased thereby. 



No ordinary light filter passes light of one wave length or 

 even approximately so ; by means of a heliostat afar more exact 

 result can be secured, especially when by the method named 

 above, a spectrum measuring 20 inches or more in length can be 

 obtained at the microscope mirror. 



Those who work with a heliostat once will anticipate further 

 sunny hoiirs for improving their acquaintance with it. 



Labelling Si'Eiimi'.ns. — It is often desirable when mounting 

 specimens to have at hand some ready means of marking them 

 for future identification. The so-called grease pencil for 

 writing on glass, which may be had in various colours, and can 

 lie purchased from many opticians, is one of the handiest and 

 neatest means, especially as the writing can be removed 

 subsequently with a little warm water. 



Another device where labels are not at hand is to pass the 

 glass slip across the tongue, allow the dam])ness to dry, after 

 which an ordinary pen and ink can be used for writing upon 

 the portion so treated. 



In the case of specimens mounted on cover glasses or slides, 

 which it IS required to identify after passing through various 

 solutions, the following method is recommen<led : — 



Mix into equal parts of egg, albumen and glycerine, sufficient 

 lampblack to make a good black fluid ; this may be used with 

 a steel pen for writing on a cover glass or slide, after which the 

 glass should be held over a flame until the ch.aracters are dry : 

 glasses so treated will not lose identification marks if placed in 

 solutions. 



PiiOTO-MlCRooitAi'HV wnii SiMi'Li; Means.— Workers with 

 limited means are often tempted to make attempts at photo 



