64 
Psyche 
[Vol. 87 
The mean number of sampled elements in the small container was 
502.2+9.7 pixels while the large petri dishes had 571.0+15.7 pixels. 
Within-group (e.g. large or small container) variation for number of 
elements did not show a significant difference (small: x 2= 0.75, ns; 
large x 2= l-72, ns) while considerable between-group variation was 
seen (Mann-Whitney test, T=0.0, p<.001). Repeated pictures of the 
same colony indicated that within-colony variation was low (0.95%). 
The small amount of within-group (large or small containers) and 
within-colony variation was due to the difficulties in representing a 
circular image with an array composed of square elements. The 
between-group variation was due to the different sizes of the 
containers. 
Most excreta located on the surface of the container were circular 
although a few irregular forms were seen. Margins were either 
smooth or undulate and color ranged from dark ebony to light tan; 
often with the central area being darker than the surrounding margin. 
The mean diameter was 1.1+0.4mm (N = 70; irregular forms were 
not measured) and there was no evidence of mold or bacterial growth 
(measured with a 10 X micrometer). 
In contrast to the above, it was very difficult to measure the 
dimensions of excreta deposited on silk as such material tended to 
flow along the silk line or adhere to adjacent threads. These excreta 
were whitish to tan in color and had a cracked appearance under 10X 
magnification. No mold or bacterial growth was seen. 
It was not possible because of the varied form and color of the 
excreta to quantify the amount of material at each deposition site by 
optical means. For this reason only the presence or absence of excreta 
was analyzed. To investigate the distribution of excreta as related to 
silk distribution, the silk density data were divided into ten levels 
(0-99, 100-199. . .900-1000 density units). No silk density data 
were greater than 1000 density units. This was necessary because 
of the relatively low number of fecal deposits in each container 
(Y= 24.6+11.0; Table 1; Fig.2). Analyzing each colony individually, 
a positive correlation was observed between the number of pixels 
within each of the ten silk-density ranges and the number of excreta 
(Spearman’s rho, p=+0.93, p<.01). In addition, examination of the 
data indicated similar distributions of excreta, animals and silk 
densities both between container sizes and among colony sizes. The 
data were therefore pooled for further analyses and a positive 
