1892.] MICROSCOPICAL JOURNAL. 37 



structure of coarse hexagonal netting, while some of the elongated and 

 boat-shaped kinds were seen to be possessed of stout ribs running at 

 right angles to the meridian line, or keel. At a later period, not 

 only was the mere magnifying power of the microscope greatly 

 increased, but, what proved to be of much more importance, 

 methods of illumination were devised which enabled the observer to 

 throw beams of light of ditlerent sorts upon the object at various angles 

 of incidence. By this means it was discovered that lined shadows 

 were cast upon the surface of valves which had previously appeared en- 

 tirely smooth and clear. It was found that these shadows are caused 

 by shallow furrows running, not only lengthwise of the valve, but also 

 at right angles to the median line or even obliqueh to it. For a long 

 time it was regarded as the acme of manipulative skill to display this 

 simple system of striation upon the larger and coarser forms upon which 

 the distance between the lines ranges from the 20,000th to the ^o, 000th 

 of an inch. By slow degrees the microscopist attained to the ability to 

 show at once two or more systems of lines, producing a cross-hatching 

 with square, lozenge, or hexagonal interspaces, and at about the same 

 time it began to be possible to discern upon some of the smaller speci- 

 mens a striation having only the So, 000th or the 90,000th of an inch be- 

 tween lines. This was the maximum of attainment about thirty years 

 ago. Since then progress has been slow in this department of micros- 

 copy and each small step achieved has caused a disproportionate 

 amount of labor and discussion. But after a while an advance was 

 made to the resolution of lines less than the 100,000th of an inch apart, 

 upon such fine species as Frustulia saxoizica and Atnphipleura pel- 

 lucida^ and the methods which rendered this progress possible brought 

 double systems of lines to view on those diatoms which had before 

 shown only one system (like Surrirella gejnma^^ and raised to the 

 rank of well-defined dots the interspaces in the previous cross-hatching 

 •upon the more robust species, such as Pleurosigma angidatHtn. Then 

 it was that microscopists ventured on the important generalization that 

 the typical form of marking, throughout the whole sub-class of diato- 

 maceffi, is a series of dots, oftenest arranged in formal rows, but some- 

 times scattered irregularly over the shell. 



Easily Obtainable. — To him who has access to running brooks, 

 quiet ponds, or the greater lakes, a range of several hundred species or 

 varieties is open. To the explorer of brackish estuaries and the deep salt 

 sea, other hundreds offer themselves. To the one who can dig into the 

 extensive deposits of their fossil remains, still other hundreds present 

 their interesting forms. But even to us who dwell within the barren 

 walls of a great city an unstinted supply of certain kinds is always close 

 at hand, for the simplest of filters applied to a Croton-water faucet 

 will, in a few minutes, furnish at least a half a dozen species; and this 

 will be our most convenient soinxe of supph'. 



Ernest Wilhelm Brucke, Professorof Physiology and Microscopic 

 Anatomy. Vienna, died Jan. 7. aged 72. Member of the Academy ot 

 Sciences and professor in Vienna since 1849. 



