The thread now becomes thicker.  The first could hardly be seen; the second is plainly visible.  The Spider shifts her position with great slanting strides, turns a few times, moving farther and farther from the centre, fixes her line each time to the spoke which she crosses and at last comes to a stop at the lower edge of the frame.  She has described a spiral with coils of rapidly-increasing width.  The average distance between the coils, even in the structures of the young Epeirae, is one centimetre. {29}

Let us not be misled by the word ‘spiral,’ which conveys the notion of a curved line.  All curves are banished from the Spiders’ work; nothing is used but the straight line and its combinations.  All that is aimed at is a polygonal line drawn in a curve as geometry understands it.  To this polygonal line, a work destined to disappear as the real toils are woven, I will give the name of the ‘auxiliary spiral.’  Its object is to supply cross-bars, supporting rungs, especially in the outer zone, where the radii are too distant from one another to afford a suitable groundwork.  Its object is also to guide the Epeira in the extremely delicate business which she is now about to undertake.

But, before that, one last task becomes essential.  The area occupied by the spokes is very irregular, being marked out by the supports of the branch, which are infinitely variable.  There are angular niches which, if skirted too closely, would disturb the symmetry of the web about to be constructed.  The Epeira needs an exact space wherein gradually to lay her spiral thread.  Moreover, she must not leave any gaps through which her prey might find an outlet.

An expert in these matters, the Spider soon knows the corners that have to be filled up.  With an alternating movement, first in this direction, then in that, she lays, upon the support of the radii, a thread that forms two acute angles at the lateral boundaries of the faulty part and describes a zigzag line not wholly unlike the ornament known as the fret.

The sharp corners have now been filled with frets on every side; the time has come to work at the essential part, the snaring-web for which all the rest is but a support.  Clinging on the one hand to the radii, on the other to the chords of the auxiliary spiral, the Epeira covers the same ground as when laying the spiral, but in the opposite direction:  formerly, she moved away from the centre; now she moves towards it and with closer and more numerous circles.  She starts from the base of the auxiliary spiral, near the frame.

What follows is difficult to observe, for the movements are very quick and spasmodic, consisting of a series of sudden little rushes, sways and bends that bewilder the eye.  It needs continuous attention and repeated examination to distinguish the progress of the work however slightly.

The two hind-legs, the weaving implements, keep going constantly.  Let us name them according to their position on the work-floor.  I call the leg that faces the centre of the coil, when the animal moves, the ’inner leg;’ the one outside the coil the ‘outer leg.’