of non-migratory Insects. 177 
songsters and butterflies were met by him several times 
in the South Sea, during gales blowing away from 
the land, and that, just as involuntarily, insects are often 
carried to the height of 15,000 to 18,000 feet above the 
plains. This illustrious savant says that the warmed 
surface of the earth causes a vertical current of air, by 
which light bodies are driven upwards, in confirmation 
of which explanation he gives the observation of M. 
Boussingault, who, together with his companion, Don 
Mariano de Rivero, saw rise from the valley of Caracas, 
whitish illuminated bodies mounting up to the height of 
5,400 feet to the summit of the Silla, and then sink to- 
wards the adjoining coast. This was at midday, and 
lasted an hour without interruption. Taken at first for 
a swarm of small birds, these bodies were afterwards 
recognized as small balls of accumulated blades of the 
grass Vilfa tenacissima.* The same author observes 
that Captain Fremont met with bees on the peak in the 
Rocky Mountains, bearing Fremont’s name, and that, 
perhaps, like the butterflies met with by himself im much 
higher regions of the Andes, also within the line of per- 
petual snow, they were involuntarily carried up by 
ascending currents of air.t Mr. Wollaston says: ‘ Un- 
willing victims,..... are ever and anon hurried to 
comparatively distant lands by the very winds that blow ; 
and not only to distant lands, but over altitudes in which 
the severity of the cold would quickly annihilate them, 
were they (as, perhaps, usually happens) to be deposited 
there on their headlong and compulsory course.” { Sir 
Charles Lyell observes that, ‘as almost all insects are 
winged, they can readily spread themselves wherever 
their progress is not opposed by uncongenial climates, 
or by seas, mountains, and other physical impediments ; 
and these barriers they can sometimes surmount, by 
abandoning themselves to violent gales, which may, in a 
few hours, carry them to very considerable distances.” § 
Our president, Mr. A. R. Wallace, has lately reminded us 
that violent gales of wind, for example, will carry bodies 
of greater specific gravity than beetles for many miles 
* A. von Humboldt, ‘Ansichten der Natur,’ 1860, vol. II. p. 30. 
¢ Ibid. Vol. I. p. 42. 
t ‘On the variation of species,’ p. 148, 1856. 
§ ‘Principles of Geology,’ 9th edit., p. 656. 
