EXTRACTS FROM FOREIGN PERIODICALS. 
377 
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 merge 
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 (MantisJ, and various other insects. They are liable to be 
devoured by parasites. Their interior forms an asylum for the larvae of insects; 
on the exterior they have to fear the larvae of Trombidions ( Tromhidium); 
finally, the Sphexes (Spkex, Linn.) make an active war on them, and stupify 
them by stinging them. 
BOTANY. 
6. 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 am dem Gebiete der theoretischen 
Erdkunde (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 
