EXTRACTS FROM FOREIGN PERIODICALS. 877 



of filaments so fine, that the slightest breeze wafted them upwards in the same 

 direction. The insect pulled it from time to time to itself, and when it felt it 

 fixed on a solid body at some distance, when the resistance and tension appeared 

 sufficiently great, it did not hesitate to dart forward on this almost imperceptible 

 bridge, doubling the thread by a fresh addition, to all appearance passing unsup- 

 ported through the air. M. Duges feels no doubt but that the fils de la vierge 

 are owing to an emission of this kind. This article closes with a description of 

 the manner in which Spiders destroy and envelop, in the substance they secrete, 

 the animals accidentally caught in their webs, when the prey is too large to be 

 immediately seized by the relentless tyrant. 



5. Mode of Attack and Defence employed by Spiders. — Lastly, in the 

 eighth section of M. Duges' interesting paper, are enumerated the means of 

 attack and defence of the Spiders, which consist principally of a poisonous fluid 

 and a hook at the end of the mandibles, which may be compared to the venom 

 of Vipers, and employed while the fluid is inserted into the wound. The bite of 

 Spiders appears incapable of inflicting serious injury to man. He has experi- 

 mented several times upon himself, and considers that the effects of the bite of the 

 Tarantula ( Tarentula), as well as of some exotic Spiders, have been exaggerated. 

 The majority of Spiders escape from their enemies by flight, and by concealing 

 themselves in holes, which, however, does not prevent their destruction, by a 

 great number of quadrupeds, birds, and insectivorous reptiles, Scorpions, Scolo- 

 pendras, Mants (Mantis), and various other insects. They are liable to be 

 devoured by parasites. Their interior forms an asylum for the larva? of insects ; 

 on the exterior they have to fear the larvae of Trombidions ( Trombidium) ; 

 finally, the Sphexes (Spkex, Linn.) make an active war on them, and stupify 

 them by stinging them. 



BOTANY. 



G. On the Botanical Geography of Swisserland, by M. Oswald Heer. — 

 During the last two years MM. Julius Frobel and Oswald Heer have published, 

 at Zurich, a journal entitled Mittheilungen aus dem Gebiete der theoretischen 

 JErdkundc (Communications relative to Theoretic Geography), of which the four 

 first numbers, forming a volume, have appeared at irregular intervals. Passing 

 over the articles on pure geography, and on zoological and geological geography, 

 many of which are well worthy of attention, we will give some account of the 

 papers on botanical geography, due to the researches of M. Oswald Heer. They 

 relate to Swisserland, but are subordinate to the general views which render 

 them valuable to the scientific men of every country. 



The first is on the relative proportion of Monocotyledons and Dicotyledons in 

 the Alpine region of the Mountains of eastern Swisserland. M. Heer having 

 determined the proportion of the two numbers in several localities, found more 



