THE ADTANCEMENT OE . SCIENCE. 73 



this term has practically been restricted to the instances in -which the in^lividual, 

 during certain phases of the change, is free and active, as in the grub of the 

 chaffer, or the tadpole of the frog, for example. In reference to some supposed 

 essential differences in the metamorphoses of insects, it had been suggested that 

 stages answering to those represented by the apodal and acephalous masgot of the 

 Diptera, by the hexapod larva of the Caribi, 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 -eases, 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; 2nd, a cocoon in the egg containing the unwinged, imper- 

 fectly-developed insect ; 3rd, the unwinged, imperfectly-developed insect in the 

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



The microscope is an indispensible instrument in embryological and histologi- 

 cal 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 microscope 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 raici-oseope 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 conifer- 

 ous 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 

 eonfervoid 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 resemblance to South American forms of these 

 organisms. Ehrenberghas recorded numerous other instances in his paper printed 

 in the 'Berlin Transactions'; but here, as in other exemplary series of observa- 

 tions of the indefitigable microseopist, the conclusions are perhaps not so satis- 

 factory as the well-observed data. He speculates upon the self developing power 

 of organisms in the atmosphere, afilrms that dust-showers are not to be traced to 

 mineral material from the earth's surface, nor to revolving masses of dust matei'ial 



