REPORTS FROM THE SECTIONS. 183 
drop of glycerine on the point of the objective, and removing the 
achromatic condenser slipped the reflex into its place, and in a 
uple of minutes had a valve of pellucida striated distinctly 
_ almost from end to end, and then carefully hunted the slide all over, 
: not a valve or fragment of a valve could I find which could 
me On removing the Tolles and puttin 
change of illumination, the latter showed the stria wherever the 
On the whole, therefore, the German glass with oblique 
Tight exhibits a resolving power on diatomaceous tests somewhat 
‘Steater than the American, and for any one making a special 
Study of the ultimate structure of the siliceous valves of diatoms, 
Objective on the oil immersion principle would be the best 
Aesame superiority on the part of the y'oth was observable on 
fab es and also on organisms in water. © For obtaining 
‘tpert Y central light I used the ach. condenser with the smallest 
wit, ve of the diaphragm behind its lenses, and a thin brass cap 
. central aperture of 45th diameters over the lenses. On P. 
with condenser as above the Tolles glass gave the best 
