32 2 American Quarterly Microscopical Journal. 



DKiES'l' OF CURRENT LITERATURE. 



^*^ JOURNAL OF THE ROYAL MICROSCOPICAL SOCIETY, 

 {April, iSjg). — THE President's Address, by H. J. Slack. — An inter- 

 esting account of the principal discoveries of the year. Observations 



on Dactylocalyx Pumiceus (Stutchbury), with a Description 

 OF A New Variety, D. Stutchburvi, by J. W. Sollas. — This article is 

 illustrated with four full plates, and several cuts in the text. It embraces 

 the results of studies carried out with specimens in the Bristol Museum _ 

 The Aperture Question, by J. Mayall, Jr. 



.j^'^^iiMay, iSyg, extra number). — A Contribution to the Knowl- 

 edge of British Orbatid^, by A. D. Michael, assisted by C. F. George. 

 — Three plates accompany the article, which gives the generic classification 

 of the members belonging to this little studied family of the Acarina. 



Notes on the Pygidia and Cerct of Insects, by 



Henry Davis. On Stephenson's System of Homogeneous 



Immersion for Microscope Objectives, by Prof. E. Abbe. The 



Vertical Illuminator and Homogeneous Immersion Objec- 

 tives, by J. W. Stephenson. — The purport of this article is to show that an 

 increase of aperture above 82" balsam is demonstrated by means of this 

 method of illumination. By reflecting a beam of light from the illuminator 

 upon an object adhering to the cover glass and removing the eye-piece, an 

 annular circle of light will be seen, surrounding a darker central space. 

 This ring of light is produced by the rays which issue from the objective 

 at an angle greater than the equivalent of 180", and it may also serve as 

 a measure of this excess. Thus, an objective having a numerical aperture 

 of 1.25 will show an annulus, the width of which will be one-fourth of the 

 radius of the central space. When these extra rays reach the under 

 surface of the cover glass, thev suffer total reflection, while the others, 

 which mark the boundary of the 180° limit, pass on. The image of the 

 rtame, therefore, which is seen when the eye-piece is used, is formed by 



the rays outside of this limit. Note on Diagrams Exhibiting 



THE Path of a Ray through Tolles' yi Immersion Objective, by 

 Professor R. Keith. — A very short note accompanying a plate of diagrams, 

 which is valuable to those who are interested in Prof. Keith's cal- 

 culations. NoteonMr. Wenham's Paper "On the Measure- 

 ment OF THE Angle of Aperture of Objectives," by Prof. R. 

 Keith. Reply to the Foregoinc; Note, by F. H. Wenham. 



**^JOURNALDE MICROGRAPHIE, (March, z^/^.)— Fecunda- 

 tion of Vertebrates, by Prof. Balbiani, (Second part.) The 



Collection of Cryptogams, by Dr. Leon Marchand. — The author is 

 adjunct professor at the Superior School of Pharmacy, in Paris, and has 

 charge of the course of Cryptogamic Botany. This lecture is highly 

 interesting, since it gives an excellent account of the work that is being 

 accomplished in the study of cryptogamic plants in this school ; and also 



