MECHANICS AND USEFUL ARTS. 29 



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 un winged, 

 imperfectly-developed insect; 3d, the unwinged, imperfectly-developed in- 

 sect in the egg, free from the cocoon, and ready to emerge. 



The microscope is an indispensable instrument in embryological and 

 histological researches, as also in reference to that vast swarm of animal- 

 cules 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 

 microscope to particular tissues and particular classes, chiefly due, in tins 

 country, to the counsels and example of the Microscopical Society of Lon- 

 don. A very interesting application of the microscope has been made to 

 the particles of matter suspended in the atmosphere; and a systematic 

 continuation 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 consist of the " pollen" or fertilizing particles of plants, and 

 have been called " pollen showers." M. Daneste, submitting to microscopic 

 examination similar dust which fell from a cloud at Shanghai, found that it 

 consisted of spores of a confervoid plant, probably Trichodesmium erythneum, 

 which vegetates in, and imparts its peculiar color 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 Ehren- 

 berg, has been shown to consist of minute organisms, chiefly " Diatomaccoi." 

 One sample collected on a ship's deck 500 miles off the coast of Africa, 

 exhibited numerous species of fresh water and marine diatoms, bearing a 

 close resemblance to South American forms of those organisms. Ehrenbcrg 

 lias recorded numerous other instances in his paper printed in the " Berlin 

 Transactions " ; but here, as in other exemplary series of observations of 

 the indefatigable microscopist, the conclusions are perhaps not so satisfac- 

 tory 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 

 meteorolites or aerolites. The advocates of progressive development may 

 see and hail in this the first step in the series of ascending transmutations. 

 The unbiased 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 

 hearers may remember the graphic description by Her Majesty's Envoy to 

 Persia, the Hon. C. A. Murray, of the cloud of impalpable red dust which 

 darkened the air of Bagdad, and filled the city with a panic. The specimen 

 he collected was examined by my successor, at the Royal College of 

 Surgeons, ^Professor Quckett, and that experienced microscopist could 

 detect only inorganic particles, such as fine quartz sand, without any trace 



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