26 
Psyche 
[March-June 
in producing the dragline (Peakall, 1969). We examined two drag- 
line attachment disks (Fig. 9) which were obtained by having 
spiders drop from glass microscope slides. Although these are not 
connections from the web, it would seem likely that mooring thread 
to non-thread substrate connections are closely related, if not equiva- 
lent, to drag-line attachment disks. 
The production of the drag-line attachment disk is attributed to 
the piriform glands (Peakall, 1969). Threads between 0.5 /i and 
1 /A thick can be seen emerging from the spools of the piriform glands 
in Fig. 10. The thinnest strands which could be resolved at the 
attachment disks were in this range of thickness (Fig. 9b). This 
thickness also corresponded to the thinnest strands of connections 
from the web. In particular, R-F’s, FY’s, and some SS-R’s had 
many strands in this range of thickness. This raises the question of 
whether the piriform glands are involved in the formation of each 
of these types of connections. One might hypothesize that some 
thread connections in the web are equivalent to drag-line attachment 
Table 6 
Descriptive statistics for some structural features of frame Y-structures 
(FY’s). For each feature, 5 FY’s from 3 webs built by 3 different spiders 
were observed. FY’s were rather variable with respect to these features, 
as indicated by the coefficients of variation. Comparing this table with 
Table 5, note the similarities 
between R-F’s 
> and FY’s. 
Feature 
Means 
Coefficient 
of Variation 
Range 
Length of Sleeve 
74.8 {X 
95 
22 jti-180 ii 
Number of Strands 
at Junction 
15-6 
60 
9-32 
Thickness of Stem of Y 
10.4 n 
24 
7 /a- 1 4 P 
Thickness of Single 
Stranded Arm of Y 
00 
bo 
“S 
19 
7 fi-IOfi 
