1901] MICROSCOPICAL JOURNAL. 105 
slides exhibited were prepared. The President then call- 
ed upon Professor Charles Stewart, who, having referred 
to the views held upon shell structure at the present day, 
and taking the common pinna shell as an example, pro- 
ceeded by the aid of drawings on the blackboard to de- 
monstrate how its structure was built. Besides studying 
the sections usually made, he recommended that the shells 
should be broken and the fractured surfaces examined, if 
a correct idea of the formation of the shells was to be ob- 
tained. 
FRESHWATER ENTOMosTRACA.—Mr. D. J. Scourfield, in 
the Proceedings of the South London Entomological and 
Natural History Society, calls attention to the value of 
Entomostraca in experimental biology. ‘‘Their common- 
ness in all parts of the country, their transparency, the 
ease with which they can be isolated and reared under all 
sorts of conditions,......mark out the Entomostraca: as 
particularly well fitted for observation in connection with 
even tlie most fundamental biological problems of the 
day.” ~-He adds: ‘We badly want detailed studies on. 
local faunas, on the seasonal distribution and variation of 
different species, on the faunas of various types of ponds, 
on the food of the most abundant forms, and many simi- 
lar subjects.” 
J. Swirt & Son’s ConDENSERS.—Messrs. J. Swift & Son 
have submitted for inspection two excellent condensers 
of their manufacture. The first is apo-chromatic, and has 
a numerical aperture of .95, Its aplanatic exceeds, how- 
ever, according to our measurements, .90 ; and as the val- 
ue of a condenser for anything approaching critical work 
depends on the aplanatic cone of light that it transmits, 
it will be seen that this condenser is eminently fitted for 
such work. As an apo-chromatic system it is, of course, 
distinctly freer from color than even the best achromatic 
system can be made, and this is very manifest when us- 
ing high-angled lenses. The power is about one-third of 
