BRITISH ASSOCIATION FOR ADVANCEMENT OF SCIENCE. 637 
acephalous maggot of the Diptera, by the hexapod larva of the Carabi, 
and by the hexapod antenniferous larva of the Meloe were really passed 
through by the orthopterous insect, before it quitted the egg. Mr. Andrew 
Murray has recently made known some facts in confirmation of this view. 
He had received a wooden idol from Africa, behind the ears of which a 
Blatta had fixed its egg-cases, after which the whole figure had been rudely 
painted by the natives, and these egg-cases were covered by the paint. No 
insect could have emerged without breaking through the case and the paint; 
but both were uninjured. In the egg-cases were discovered — 1st, a grub- 
like larva in the egg ; 2d, a cocoon in the egg containing the unwinged 
imperfectly-developed insect ; 3d, the unwinged, imperfectly-developed 
insect in the egg, free from the cocoon, and ready to emerge. 
Value of the Microscope. 
The microscope is an indispensable instrument in embryological and histo- 
logical researches, as also in reference to that vast swarm of animalcules 
which are too minute for ordinary vision. I can here do little more than 
allude to the systematic direction now given to the application of the micro- 
scope to particular tissues and particular classes, chiefly due, in this country, 
to the counsels and example of the Microscopical Society of London. A 
very interesting application of the microscope has been made to the par- 
ticles of matter suspended in the atmosphere ; and a systematic continua- 
tion of such observations by means of glass slides prepared to catch and 
retain atmospheric atoms, promises to be productive of important results. 
We now know that the so-called red-snow of Arctic and Alpine regions is a 
microscopic single-celled organism which vegetates on the surface of snow. 
Cloudy or misty extents of dust-like matter pervading the atmosphere, such 
as have attracted the attention of travellers in the vast coniferous forests 
of North America, and have been borne out to sea, have been found to con- 
sist of the “pollen” or fertilizing particles of plants, and have been called 
“pollen showers.” M. Daneste, submitting to microscopic examination 
similar dust that fell from a cloud at Shanghai, found that it consisted of 
spores of a confervoid plant, probably the Trichodesmium erythrceum, which 
vegetates in, and imparts its peculiar colour to, the Chinese Sea. Decks of 
ships, near the Cape de Verde Islands, have been covered by such so-called 
“showers” of impalpable dust, which, by the microscope of Ehrenberg, has 
been shown to consist of minute organisms, chiefly “ Diatomacese.” One 
sample collected on a ship’s deck 500 miles off the coast of Africa exhibited 
numerous species of freshwater and marine diatoms bearing a close resem- 
blance to South American forms of those organisms. Ehrenberg has re- 
corded numerous other instances in his paper printed in the * Berlin Trans- 
actions but here, as in other exemplary series of observations of the 
indefatigable microscopist, the conclusions are perhaps not so satisfactory 
as the well-observed data. He speculates upon the self-developing power of 
organisms in the atmosphere, affirms that dust-showers are not to be traced 
to mineral material from the earth’s surface, nor to revolving masses of 
dust material in space, nor to atmospheric currents simply ; but to some 
general law connected with the atmosphere of our planet, according to 
which there is a “self-development” within it of living organisms, which 
organisms he suspects may have some relation to the periodical meteoro- 
lites or aerolites. The advocates of progressive development may see and 
hail in this the first step in the series of ascending transmutations. The 
unbiassed observer will be stimulated by the startling hypothesis of the 
celebrated Berlin Professor to more frequent and regular examinations of 
atmospheric organisms. Some late examinations of dust-showers clearly 
show them to have a source which Ehrenberg has denied. Some of my 
