oe a ee he oe, 
a ee Tee. See ee a ee ee J = ¢ + J 
CONSTRUCTION OF AN ORBWEB. a 
the spider uses her limbs as a measure to regulate the distances of her 
radii or “wheel spokes,” and the circular meshes interweaved into them.! 
The above method of alternate apposition shows that the dis- 
Legsno tances between radii, at least, are not determined by any such men- 
Unit of ' P ee 
Measure, S##tion, which of course would only apply on the supposition that 
the lines were spun consecutively. Moreover, having frequently 
measured the distances between the radii at their circumference or attach- 
ment to the foundation lines, I have found that there is often great irreg- 
ularity therein; the interspaces sometimes vary in the proportion of three 
to one on the same orb. The fact that the number of radii is not con- 
stant in the successive webs of any individual spider, but varies from day 
to day (although within a narrow limit), is also against this hypothesis. 
It has already been intimated that the notched zone serves an important 
end in bracing the radii while they are yet in outline. This appears dis- 
tinctly while observing the above described behavior. The first 
Forming yadii that are inserted bend and sway under the weight of the 
Notched : : é E 
Rote, spider, which, as she clambers over them, suggests the idea of a 
carpenter engaged upon a scaffolding in its first crude state. 
In some cases the aranead stops at the guidon, after having placed the first 
few radii, and swings her spinnerets around their bases as though to 
strengthen them. This act may be repeated several times; and in fact the 
spider whenever she comes to the centre is apt to make two or three of 
these gyrations. However, when all the radii are inserted she proceeds to 
complete the notched zone, laying in the spirals thereof from the centre 
outwardly. These vary in number from four or five to ten or even more. 
This variation holds in webs of the same species; for example, in seven webs 
of Argyroepeira hortorum, the spirals in the notched zone numbered, suc- 
cessively, 8, 10, 10, 10, 6, 8, 5. I have counted as many as twenty in the 
web of Epeira gibberosa, In the group of Orbweavers, of which Epeira 
insularis? is the type, the number of notched spirals is quite persistently less, 
commonly five or six. The width of the notched zone is about equal to, or 
a little greater than that of the free zone, and about twice that of the hub. 
In at least one example noted (an orb of Tetragnatha extensa) three wide 
notched spirals were first spun before the others were laid in. These ap- 
peared to be the analogue of the spiral scaffold, referred to in the next 
section; but this is not the ordinary rule of construction. 
Mr. Romanes* quotes Dr, Leach as giving, on the authority of Sir J. 
Banks, a case of a web-spinning spider which had lost five of its legs, 
1Tnsect Architecture, page 313, 
* This familiar and beautiful spider Dr. Thorell declares quite identical with the Epeira 
marmorea of Europe. I have no specimens of E. marmorea with which to compare, but 
have no doubt of Dr. Thorell’s identification. However, I retain Hentz’s name in the two 
volumes on Habits, and will endeavor to adjust the nomenclature of this and other species 
in the final volume. 
® Mental Evolution in Animals, page 209. 
