459 Mr. BLACKWALL’s Observations to ascertain 
usual horizontal position into one almost perpendicular, they 
emitted from their spinning-apparatus a small quantity of the 
glutinous secretion with which they construct their webs. This 
viscous substance being drawn out by the ascending current of 
rarefied air: into fine lines several feet in length, was carried 
upward, until the spiders feeling themselves acted upon with 
sufficient force in that direction, quitted their hold of the objects 
on which they stood, and commenced their journey by mount- 
ing aloft. z | 
Whenever the lines became inadequate to the purpose for 
which they were intended, by adhering to any fixed body, they 
were immediately detached from the spinners, and so converted 
into terrestrial gossamer by means of the last pair of legs, and 
the proceedings just described were repeated ; which plainly 
proves that these operations result from a strong desire felt by 
the insects to effect an ascent. But what, it may be asked, is 
the exciting cause of this singular propensity? It has been 
suggested that hunger, or an inclination to procure some fa- 
. vourite kind of food, may supply the requisite stimulus. These 
suppositions, however, are discountenanced by the plump ap- 
pearance which the animals exhibit; by their total disregard 
of such winged insects as happen to be placed within their 
power; by their utter inability to regulate their motions, while 
afloat, in any other manner than by letting out or drawing in the 
lines by which they are conveyed through the air, and thus pro- 
moting their ascent or descent; by the unsuitableness of the 
lines for securing their prey; and lastly, by the uncertainty 
when a favourable day for their purpose may occur, or even 
that one may occur at all. 
Were I to hazard a conjecture on the subject, I should be 
disposed to attribute the manifest anxiety of these insects to 
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