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PKOGKESS OF MICEOSCOPICAL SCIENCE. 
Diatomacece in the Carboniferous Epoch, by Count Castracane. 
' Transactions of the Academia dei nuovi Lincei.' Rome. February, 
1875. — The remains of several species of Diatomaceaa were discovered 
in coal by the following method. A portion of the solid interior was 
reduced to a coarse powder, and burned in a small porcelain vessel in 
a glass tube, through which a stream of oxygen was passed, but the 
temperature was kept as low as possible, in order to avoid any fusion 
of the ashes. These were then heated in a mixture of nitric and 
hydrochloric acids with some chlorate of potash, in order to remove, 
as far as possible, all impurities. On carefully examining the residue 
thus obtained from various specimens of coal from different localities, 
mostly British, Diatomacege were invariably found, though usually only 
in small numbers. All agree with known living species in form 
and in the number of the markings, and in fact in every particular. 
Some specimens yielded marine, but the greater number fresh-water 
species. The author appears to have taken every precaution to avoid 
being misled by the presence of accidental impurities, and he points 
out the importance of the facts in connection with the origin of coal, 
and as showing that such low organisms have continued to exist with 
the same constant characters for such a vast geological period. In 
conclusion, it may be named that the author has kindly sent for 
exhibition at the meeting of the Royal Microscopical Society, two 
mounted specimens, showing well-marked Diatomacese and other 
interesting minute organic remains. 
On " Personal Equation " in Microscopy. — Those who are familiar 
with astronomical matters will readily understand the above expression. 
But to the microscopist it will be almost entirely new. Mr. J. Ingpen, 
the Secretary of the Quekett Club, has a very important paper on this 
subject in the last number (March) of the ' Journal of the Quekett 
Club.' He points out the many varieties of this "equation," which 
must be taken into consideration in every instance, and he explains 
by numerous examples the several optical differences of observation 
under the heads of colour, focus, and form. The paper must be read 
itself, as it is impossible to briefly abstract it. The discussion to 
which it gave rise is also of much importance, the President's (Dr. 
Matthews) remarks being of much interest. 
Influence of Light on Development. — This subject has been examined 
from time to time with the most contradictory results, and in nearly 
all cases it is the young of the frog that has been examined. M. Thury 
has been recently examining this question. He took the eggs of Bana 
temporaria and placed them all under precisely the same favour- 
able circumstances, except that while part received light through 
colourless glass, another part received it through green glass. The 
former developed rapidly, and by the end of May had a length of four 
centimeters, and well-developed hind legs in most of them ; while the 
latter were slowly developed, blackish in colour, hardly had a length 
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