CONSTRUCTION OF AN ORBWEB. 75 
lines which net the enclosed space have such an entan- 
glement with the guidon ball as to brace it sufliciently 
from beneath, the spider instead of dropping down may 
first climb up the radius a, carrying a free thread in 
one of her hind feet which is held out quite well from 
the radius for this purpose as shown at Fig. 71. When 
a desired point of attachment, as K, has been reached, wo. 71. Putting ina 
the deported line x is drawn taut, fastened, and the radius ips 
e is now formed, which in this case will be the second radius. Next the 
spider returns to the guidon H by e, or more likely by a, and thence 
drops to the line, mn (Fig. 69), forming a third radius, ¢. The radii are 
all inserted in the above manner, and not consecutively, but alternately on 
the opposite sides of the included space, by single lines or successive coup- 
lets. The behavior of different’ individuals of the same species or of the 
individuals of different species may show variations more or less decided, 
but the above action is fairly typical. 
Blackwall says! that the radii are formed by the spider “ without 
observing any regularity in the order of her progression.” On the con- 
trary there seems to be at least so much order in this act that a 
Alternate gort of alternation as to the orientation of the lines is observed, 
eee which I have called the alternate apposition of the radii. A 
Radi. purpose to maintain a balance in the radial framework during 
its construction is thus suggested, although, certainly, an absolute 
regularity of alternate progression cannot be asserted. 
The order in which the radii are spun into the frame of the orb was 
quite fully shown in the work of an Epeira sclopetaria observed at Alex- 
andria Bay, New York. When the observation began the foundation lines 
were already laid, and also the original radii 
marked A, B, C, D, Fig. 72. These cords were 
united at the centre by a tuft of silk, and 
braced by a few concentric lines, which form- 
ed the basis of the hub. I counted seventeen 
radii before the spider ceased. Their alter- 
nate apposition can easily be seen by tracing 
them in the order of the numerals in Fig. 72, 
which are arranged in the order of construc- 
tion. That is, radius 1 was formed by car- 
rying the line along D to 1 and tightening it. 
Thence the spider went to the centre, ran 
along B, which had previously been inserted, 
thence down to 2, where the radius 2 was 
Fic, 72, Alternate apposition of radii, formed. Irom 2 again she went to the centre, 
1 Op. Cit., page 182, 
