914 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. NXVIll 
and elaborate degree, even in the complexity of delicate movements that enter 
into the manufacture of this spiral line. 
There is still a further point to consider before we leave this portion of the 
snare. By what mechanism does the Nephila measure the even distance be- 
tween her coils ? She is a skilful geometrician, and she must have some very 
efficient method of securing the perfect parallelism of her lines. Again I recall 
the work of the Araneus. She is so swift, so agile in all her movements ; she 
fixes her line so rapidly that it is difficult to observe with minute care the mode 
of measurement whicli she adopts. Nevertheless, I found by the aid of ex- 
periment that she works on a very simple plan. She converts her fore leg into 
a measuring rule in order to estimate the distance between the turns. While 
she is engaged at one turn she stretches out her fore leg until with the extreme 
tip she touches the turn which she laid down in her last circle. In this way she 
measures off a certain distance from her last turn and then she affixes her thread. 
At every point of fixation she makes the same measurement ; thus she ensures 
that the new line is parallel to the one last laid down. 
Let us look now to the slow and leisurely Nephila. There is no haste about 
her grave actions. She will surely tell us something ; she is so decided in every- 
thing she does. It is immediately evident that her mode of operation is quite 
distinct from that of the Araneus. At no time does she bring her fore leg so 
is to touch her viscid spiral ; indeed, I have already shown that these legs are 
employed in another way. We must look to the hind leg of the Nephila in 
order to discover how the measurement is made. 
I fear that I am very tedious, but it is worth observing this geometrical act 
with a little detail and care. The Nephila is circling to the left. Four turns 
of her viscid spiral are in place, and she is now engaged in anchoring the fifth. 
I have already explained how the hind leg on the left side receives the radius 
from the third leg, and then draws the line steadily in until it touches the spin- 
nerets. But let us fix our attention at the very moment of this act. The 
hind leg receives the radius ; the line is clutched in the terminal claws ; but the 
essential point to observe is that the claws take hold of the I’adius at the exact 
point where it meets the fourth turn of the spiral, that is the turn which has 
last been laid down. From that point it draws in the radius until the line comes 
in contact with the spinnerets about one-sixth of an inch away. The spider 
passes on from radius to radius, and at every anchorage the same mechanism 
occurs. The tip of the hind leg always takes hold of the radius at the point 
where it meets the last turn of the spiral. And as the leg is kept bent in the same 
position an equal distance is thus always measured off. It is the distance from 
the spinnerets to the tip of the hind leg. Thus each line is the same distance 
from each preceding line, and a perfect parallelism is secured. It is a very 
simple mechanism, but it is wonderfully precise. It stamps the Nephila as 
an accurate geometrician that works in a mathematical way. 
It is only by some such simple mode of measurement that this excellent result 
could be obtained. For remember that the Nephila is an ungainly creature 
with slender groping limbs that span over six inches across. Yet with such 
long and awkward implements see what a marvellous net does she produce. 
Every line is in perfect parallel, and they are only one-sixth of an inch apart ! 
By the aid of two experiments I confirm the fact that this is the mode of 
measurement employed to draw line parallel to line. The first experiment is 
a mere repetition of one previously made on the snare of the Araneijis. It 
fixes the junction of the last turn of the viscid spiral with the radius as the 
point from which the measurements are made. For if the spider places one 
turn by estimating the distance from this junction on the preceding turn, then 
if I remove the preceding turn, I will deprive her of this junction ; I will have 
taken away her point of measurement, and, as a result, she should fail 
to draw parallel lines. I perform the experiment ; I remove the turn in one 
