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THE ARMATURE OF ORBWEBS: VISCID SPIRALS. 89 
When drawn out by the foot of the spider into the position of x-ab, 
Fig. 80, how is this viscid matter affected? In order to test the effect 
of expansion and sudden contraction upon viscid matter spread along a 
line, I covered thin bands of India rubber with mucilage, and then sud- 
denly stretched them, The result was that invariably globules or beads 
were formed similar in shape to those upon the spiral of an orbweb. A 
twist of the band, by rolling it between the finger and thumb, caused the 
globules to mass equally around the band, a position which they would 
doubtless have kept permanently, as do the spider’s beads, could the muci- 
lage have hardened as rapidly as the viscid secretion from the spider does. 
This tendency would probably be greatly increased were the spider when 
emitting the viscid matter to give the line a sharp twist or even impart to 
it a vibratory motion. At all events, we know that an elastic line drawn out 
in the above manner and suddenly released is set into vibration, the mechan- 
ical effect of which would certainly be in the direction here indicated. 
However, it is probable that a natural contraction or crystallization of 
the viscid matter itself would follow when exposed to the air, and thus 
produce the beads without any mechanical agitation, which 
Natural nevertheless would undoubtedly assist the action of aggregation. 
Crystalli- ; ; h a th lnstie ti Tests 
mation, Various experiments showed that an elastic line, or elastic band, 
when covered with mucilage and then stretched, soon becomes 
threaded with a series of beads not unlike those on the web of the geo- 
metric spider. The natural tendency of the material is evidently to gather 
into these minute globular masses. If we suppose this to represent a gen- 
eral tendency of viscid liquids, we have at once the reason why spiral 
lines covered with viscid secretion as they are emitted, should soon present 
the appearance of strings of beads. 
Incidentally it may be said that the elasticity of the beaded spiral en- 
ables the spider to so graduate the interradials that they are all taut. 
The fact that the radii converge upon the centre compels a 
Soe great difference in length between a string drawn at the outer 
eat. margin and one at the interior. Does it not imply a great de- 
gree of mathematical skill to pay out the requisite amount of 
line as the distances gradually and continuously diminish? I suppose that 
the whole matter is solved chiefly by the elasticity of the spiral thread. 
If the spider were to draw out an equal length of line in every case it 
would bridge the wider interspace at the circumference and the narrower 
one at the centre with equal facility. 
What is the condition of the spiral thread as it escapes from the spin- 
nerets? Does it show at once the appearance of viscid beads? 
How Or, is it smooth upon the surface, and do the nodules gradually 
BOaOH B78 fter emission? The difficulty of finding < ider at the 
Mute: orm after emission ? re di y iding a spider 
exact point of spinning necessary for this observation is in itself 
considerable; to find a web so located as to allow study under a glass of 
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