ENGINEERING SKILL OF SPIDERS. 
in addition the spider began to run up and down 
her snare, the pebble was simply lifted up by the 
tightening of the upper lines of the snare. This 
result was probably assisted by the natural con- 
traction of the elastic threads, and by the pulling 
of the shrubbery under the force of the wind. 
My conclusion was, therefore, that the spider had 
balanced her 
orb in the 
usual way, 
but discoyer- 
ed that, al- 
though it was 
“founded up- 
on a rock,” 
her house was 
rendered in- 
secure by the 
simple fact 
that the rock 
was not able 
to keep its 
place against 
the strain. 
Mrs. Kigenmann sent me from Southern California some 
cocoons of Zilla x-notata, from which I succeeded in raising 
a number of broodlings, who domiciled in my 
ee library. Many tiny snares were woven upon a 
ea : 
otted ivy plant, : I these gave an ex- 
Counter. Potted ivy plant, and one of these gave an e 
poise, ample of ready adaptation. The stay lines of 
the orb were attached to sundry leaves, and the 
upper and side attachments proved secure. But the leaf 
to which the whole lower system of supports was fastened 
fell off and stretched them downward, giving the snare a 
peculiar, elongated shape, which I have never seen quite 
approached. (Fig. 202.) This swinging pedestal amply 
served the purpose of the wee architect, whose frail web 
(drawn here natural size) was well balanced even by so 
light a weight. The weaving went on upon this new 
basis, radii were spun down into the elongation, and 
when the spiral loops were put in, that part was not 
omitted. Thus, the net space available for business was 
a good deal enlarged, and what was lost by the free 
sector at the top was quite made up by the netted 
FiG. 202. Sectoral orb of Zilla counterpoised by a fallen ivy leaf. 
