262 ON AERONAUTIC SPIDERS. 
occur at all. Were I to hazard a conjecture on the 
subject, I should be disposed to attribute the manifest 
anxiety of these animals to change their quarters to a 
feeling of insecurity occasioned by their proximity to 
one another, the prodigious numbers which in 
favourable seasons are usually congregated together 
affording the more powerful individuals an opportu- 
nity, seldom neglected by these voracious creatures, of 
making an easy prey of the weaker ; and this opinion 
is strengthened, if not confirmed, by the fact that they 
are chiefly spiders which have not arrived at maturity 
that undertake these migrations. 
I have asserted that when Aéronautic Spiders per- 
form their aérial journeys they are borne upwards by 
an ascending current of rarefied air impinging against 
the slender lines which proceed from their spinners. 
I shall now endeavour to demonstrate that this curi- 
ous atmospherical phenomenon, which well deserves 
the attention of meteorologists, affords them the only 
available means of accomplishing their object, and 
that the hypotheses previouly adverted to are quite 
ureconcilable with facts, and, consequently, must be 
erroneous. 
It has been already stated that gossamer is never 
seen floating in the air except in calm sunny weather ; 
its buoyancy, therefore, evidently does not depend 
upon the agency of winds, usually so called: indeed 
it is probable that winds never do take an upward 
direction, unless influenced by some extraordinary 
