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PKOGRESS OF MICROSCOPICAL SCIENCE. 
Atmospheric Dust . — The ‘Academy’ (May 8) says that a micro- 
scopical examination of atmospheric dust which fell in parts of 
Sweden and Norway on the night of March 29-30, 1875, has led 
M. Daubree to believe that it proceeded from a volcanic eruption in 
Iceland, as it closely resembled the pumice powder from that country, 
and especially that of Hrafftnurhur. M. Nordenskidld, telegraphing 
from Stockholm, said : “ Grey vitreous and fibrous powder fell here 
with snow on March 30 : several grammes collected.” M. Kjerulf 
sent to M. Daubree a specimen of the same dust collected from the 
snow by Dr. Kars, between Sondmore and the valley of Romsdal in the 
west, and Tryssil, in the direction of Stockholm, in the east. The dust 
was found to be composed of fragmentary transparent grains, some 
colourless, others more or less brownish yellow. Most of them were 
finely striated, fibrous, and full of vesicles, round or elongated, the 
latter being most common. Few of these reached the dimension 
of t 2 0 millimeter in length, and many were only from to 
3 ^^ millimeter. M. Daubree also recognized minute crystals of 
pyroxene and felspar. He reminded the French Academy of several 
instances of dust being conveyed by air-currents to great distances. 
Thus in February, 1863, sand, apparently from Sahara, fell in the 
western parts of the Canaries, transported 32 myriameters ; and more 
recently, ashes from the Chicago fire reached the Azores in four 
days, accompanied with an empyreumatic odour, which made the in- 
habitants suppose that a great forest was in conflagration. In 1783 
the dry fog, which covered most of Europe for three months, was 
occasioned by dust from an Iceland eruption. 
The Functions of the Frontal Ganglion in Dytiscus . — The functions 
of the frontal ganglion of Dytiscus marginalis are elucidated by 
M. E. Faivre in a paper which will be found in ‘ Comptes Rendus ’ 
(May 31, 1875). After detailing a variety of experiments, he states, as 
a result of his researches, that “ the frontal ganglion specially pre- 
sides over the movements of deglutition, determining not only the 
contraction, but also the dilatation of the pharyngeal sphincter, 
while it reacts at the same time by the recurrent nerve on the 
cardiac sphincter. The action of this nervous centre may be excited 
by impressions from back to front or the opposite. It associates 
together by means of its connection with the encephalon, acts of pre- 
hension, mastication, pharyngeal deglutition, and ingestion of food to 
the stomachs and the intestine. The suboesophagal ganglion is the 
centre, under the influence of which it reacts with the most energy. 
In fine, the frontal ganglion, distinguished by special functions from 
all other nervous centres of the ganglionic chain, is allied to them 
by its essential properties, and, as we may be assured, by its structure 
also.” — See Academy, June 12. 
The Development of the Nervous System in Limulus . — A very valuable 
paper on this subject was read by Mr. A. S. Packard, jun., before the 
