1979] 
Chaffee & Tarter —- Baetisca bajkovi 
55 
gram was used to show the monthly variation in head widths 
(Hubbs and Perlmutter, 1942). The growth rate of the nymphs 
(sexes combined) was determined by using the mean monthly head 
width measurements. 
Relative abundance of foregut contents of the nymphs was deter¬ 
mined for each month. Five nymphs were selected at random from 
each month’s sample for analysis. Micro-dissecting scissors were 
used to sever the head and make an incision along the midline of the 
ventral surface. The foregut was then severed from the intestine and 
excised. The foregut contents were extruded onto a glass slide and 
examined under a microscope with a Whipple ocular grid at 430X 
magnification. Five grids or fields were randomly selected to be 
examined for each nymph. The percentage of composition for each 
food item was determined by figuring the percentage of small grid 
squares within each field that contained each of the different food 
items. Percentage composition was determined for the following 
food items: (1) plant detritus, (2) diatoms, (3) filamentous algae, and 
(4) mineral particles. 
The sex of the nymphs was determined by the size and shape of 
the eyes. The eyes of the male are much larger and positioned more 
closely together than those of the female. The chi-square test was 
applied to the nymphs to determine any significant departure from 
the 1:1 ratio at the 0.05 confidence level. 
The last instar nymphs collected in April and May were returned 
to the laboratory for rearing. They were observed closely, and the 
dates and times of emergence for both the subimagos and imagos 
were recorded. 
The fecundity of B. bajkovi was determined by direct egg counts 
of the adult females using a Bausch and Lomb dissecting micro¬ 
scope. Using micro-dissecting scissors the body cavity was carefully 
opened with a long dorsal incision. Both ovaries were then carefully 
excised and the eggs extruded into a culture dish for counting. Size 
measurements were made on 25 eggs from each female with an 
ocular micrometer in a dissecting microscope to the nearest 0.01 
mm. The external morphology of the eggs was also viewed under a 
microscope at 100X magnification. 
Results and Discussion 
Stream Environment. The mean annual water temperature in 
Beech Fork during the study period was 13.5 C. The monthly ex- 
