1980] 
Morris, Chaffee, & Tarter — Baetisca 
41 
together. Diatoms and filamentous algae were grouped as separate 
catgories. 
A habitat preference study on nymphs was designed. A tray (61 X 
30.5 X 6.5 cm) was filled with 2.5 cm of water from the study area. The 
bottom of the tray was filled with three different substrates. One- 
third was filled with sand only, one-third with sand, gravel and small 
rocks and one-third with sand and leaf litter. The water was 
constantly aerated with a Hush air pump and the tray was placed in a 
controlled chamber which kept the water temperature at 11 C. The 
nymphs were then released at different places in the tray. After 12 
hours of darkness, the tray was checked for the location of the 
nymphs. The entire tray was then illuminated with a light placed so 
that it shone equally on each area. After 12 hours, the nymphal 
positions were checked. The second part of the experiment involved 
shining the light directly on one area, while the other two areas were 
covered. After 12 hours, the position of the nymphs was recorded and 
another area was illuminated. The entire experiment was then 
replicated. 
Direct egg counts of four subimagos and three imagos from lab 
rearings were made. These adults had been preserved in 70 percent 
ethanol. The body cavity was opened with micro-dissecting scissors 
and the eggs were carefully extruded into a culture dish and counted 
under a Bausch and Lomb dissecting microscope. The diameter of 50 
eggs per female was measured with an ocular micrometer mounted in 
a microscope to the nearest 0.01 mm. 
Results and Discussion 
Stream Environment.—The water quality of Laurel Fork was 
excellent for aquatic life. Dissolved oxygen concentrations ranged 
from 10 (June-August) to 14 mg/1 (February and April); the mean 
was 11.9 mg/1. Carbon dioxide was 5 mg/1 during all months except 
November (10 mg/1). Total hardness ranged from 34.2 mg/1 in 
February, March and October to 68.4 mg/1 in May and June; the 
mean was 49.7 mg/1. Bicarbonate alkalinity values ranged from 13.7 
to 51.3 mg/1. February and May-September, respectively; the mean 
was 37.6 mg/1. The hydrogen ion concentration (pH) ranged from 7.5 
to 8.5; the mean was 8.1. The mean annual water temperature was 
11.6 C; the range was 2.8 to 22.0 C, January and August, respectively. 
