1980 ] Tietjen — Sanitary Behavior of Malios gregalis 
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elements (=1024 pixels)-, however, a mask which simplified position 
analysis reduced the actual number of elements used in statistical 
analyses to 502 ± 10 pixels for the small and 571 ± 16 pixels for the 
large petri dish (Fig. 1). The camera was located ,65m from the 
recording surface providing a field of view for each pixel of 3.8mm 2 
(about the size of a mature female M. gregalis). 
The density of silk at each of the 1024 positions within the 
container was recorded by programming the computer to begin at a 
short exposure time (13ms) and record in computer memory the 
positions of those pixels activated by light. The exposure time was 
then increased in ,03ms increments 1024 times. Each iteration 
resulted in darker areas in the field of view being recorded. This 
resulted in a grey-level representation of the image in 1024 levels at 
each of the positions. Because silk blocked out light, grey-level and 
silk density were inversely proportional. 
To compensate for possible uneven lighting effects and to scale the 
data to silk-density at each point, the above data were subtracted 
from base-level information obtained by taking a grey-level picture in 
Figure 1: Computer-controlled camera equipment designed to record the distribu¬ 
tions of animals and excreta as related to silk densities. Transmitted light (L) is 
provided by a light source and a refector (R) with a diffusion screen (D). Light passes 
through a transparent red plastic filter (F) and is reflected by an opaque white plastic 
mirror (M) which provides for further diffusion of the light. The light passes through a 
clear plastic base (B) and into a petri dish (P) which holds the experimental colony. An 
opaque mask blocks light outside the colony recording area and a hood (H) 
surrounding the recording area reduces the ambient light level seen by the camera (C). 
The camera is controlled by a computer which also receives the image data. This 
information is transmitted to a second computer for numerical analyses. 
