184 Mr. Blackwall on the Construction of the 
ceal herself from observation. From the centre of the net to this retreat 
she spins a line of communication, composed of several threads united 
together throughout their entire length, the vibrations of which speedily 
inform her of the capture of her prey; and here her labours terminate. 
Such is the process, with some slight modifications now to be noticed, 
employed by the geometric Spiders in the formation of their snares. One 
species generally converts a radius into the line of communication between 
the net and its retreat, instead of spinning a separate line for that pur- 
pose ; and this peculiar appropriation, whether the radius be in the plane 
of the snare, or whether it be withdrawn from that plane, as is frequently 
the case, imparts an unfinished appearance to the net, as it prevents the 
spider from giving her viscid line a spiral form, though this is sometimes 
attempted with a greater or less degree of success. No sooner does the 
Spider arrive at one of the radii adjacent to that in connection with her 
cell, than she returns, traversing the frame-work of her snare till she 
arrives at the adjoining radius on the opposite side, when she again re- 
traces her steps, and thus oscillating between the two, spins a number of 
curved viscid lines, or arcs of circles, diminishing in length from the 
circumference of the net towards the centre. Dr. Lister, who has figured 
and described this species in his Treatise de Araneis, fig. X. p. 47-8, was 
well acquainted with this peculiarity so common in the structure of its 
snare, but he has fallen into the error of supposing that it occurs invari- 
ably, as appears from the following passage cited from his work. ‘* Rete 
“ amplum & elegantissimum tendit : illud autem in eo perpetuum & sin- 
“* gulare est, nimirdm é radiis unicum maculis utringque nudari, idque é 
** centro reticuli ad ejus usque circumferentiam ; qui feré ad aliquam in 
‘¢ pariete rimulam aut alibi, ubi animal tuté totum diem latet, porrigitur : 
“© atque hic radius ei velut scala est, per quem ascendat descendatque.”’ 
The learned authors of the Introduction to Entomology, in treating 
upon the construction of the nets of geometric Spiders, (for their remarks, 
though limited to the proceedings of an individual for the convenience of 
description, seem intended to apply to all,) state that the Spider always 
leaves a vacant interval round the smallest first spun circles that are 
nearest the centre, but for what purpose they are unable to conjecture ; 
and that lastly, she bites away the small cotton-like tuft that united all the 
radii at the centre of the net, and in the circular opening resulting from 
