THE ENTOMOLOGIST’S WEEKLY INTELLIGENCER. 
127 
rent occasioned by the rarefaction of the 
air contiguous to the heated ground. 
Against these lines the current of rarefied 
air impinges, till the animals, feeling 
themselves acted on with sufficient force, 
quit their hold of the objects on which 
they stand, and mount aloft. 
“ Spiders do not always ascend into 
the atmosphere by a vertical movement, 
but are observed to sail through it in 
various directions; and the fact admits 
of an easy explanation, when the dis- 
turbing causes by which that subtile 
medium is liable to be affected are taken 
into consideration. A direction parallel 
to the horizon will be given by a current 
of air moving in that plane; a perpen- 
dicular one, by the ascent of air highly 
rarefied; and directions intermediate be- 
tween these two will, in general, depend 
upon the composition of forces. When 
the horizontal and vertical currents are 
equal iu force, the line of direction will 
describe an angle of 45° nearly with the 
plane of the horizon; but when their 
forces are unequal, the angle formed with 
that plane will be greater or less as one 
current or the other predominates. 
“ The manner in which the lines are 
carried out from the spinners by a cur- 
rent of air appears to be this. As a pre- 
paratory measure, the spinning mam- 
mulae are brought into close contact, and 
viscid matter is emitted from the papillae; 
they are then separated by a lateral 
motion, which extends the viscid matter 
into fine filaments connecting the pa- 
pillae ; on these filaments the current im- 
pinges, drawing them out to a length 
which is regulated by the will of the 
animal, and on the mammulae being 
again brought together the filaments 
coalesce and form a compound line. 
“ Many intelligent naturalists enter- 
tain the opinion that spiders cau forcibly 
propel or dart out lines from the spin- 
ners ; but when placed on twigs set up- 
right in glass vessels with perpendicular 
sides, containing a quantity of water 
sufficient to immerse their bases com- 
pletely, all the efforts they make to effect 
an escape prove unavailing in a still 
atmosphere. However, should the indi- 
viduals thus insulated be exposed to a 
current of air, either naturally or arti- 
ficially produced, they immediately turn 
the abdomen in the direction of the 
breeze, and emit from their spinners a 
little viscid secretion, which being car- 
ried out in a line by the current becomes 
connected with some object in the vicinity, 
and affords them the means of regaining 
their liberty. If due precaution be used 
in conducting this experiment, it plainly 
demonstrates that spiders are utterly in- 
capable of darting lines from their spin- 
ners, as they cannot possibly escape from 
their confinement on the twigs in situa- 
tions where the air is undisturbed, but in 
the agitated atmosphere of an inhabited 
room they accomplish their object without 
difficulty. Similar means are frequently 
employed by spiders in their natural 
haunts for the purposes of changing their 
situation aud fixing the foundation of 
their snares. 
“ The webs named gossamer are com- 
posed of lines spun by spiders, which, on 
being brought into contact by the me- 
chanical action of gentle airs, adhere 
together, till by continual additions they 
are accumulated into irregular white 
flakes and masses of considerable magni- 
tude. Occasionally spiders may be found 
on gossamer webs, after an ascending 
current of rarefied air has separated them 
from the objects to which they were 
attached and has raised them into the 
atmosphere ; but as they never make use 
of them intentionally in the performance 
