LIMNOLOGICAL STUDIES OF KARLUK LAKE 
429 
ference in the diatoms. On July 12 and 13, 1928, the average numbers down to 50 and 
45 meters, respectively, were substantially the same at station 1 and at station 2 for 
the green algse and the rotifers, but the diatoms were about five times as abundant 
at the latter as at the former station. The nauplii were a little more than five times 
as abundant at station 1 as at station 2. On July 12 and 13, 1930, there was sub- 
stantially the same average number of rotifers, nauplii, green algae and diatoms in 
the upper 50 meters at station 1 as in the 45-meter series at station 2. 
Similar variations in numbers were noted between the catches taken at station 1 
and those at station 3. On July 19, 1927, the average number of nauplii down to 
50 meters at station 1 was 44 per liter and 19 per liter at station 3; the rotifers num- 
bered 350 per liter at station 1 and 360 at station 3. The green algse were five times 
and the diatoms four times as numerous at station 3 as at station 1. On July 9, 
1929, the catches in the upper 50 meters at station 1 yielded a larger number of net 
plankton organisms than those at station 3; the difference was less than twofold 
in the rotifers and the green algae, but it was fourfold in the nauplii and fivefold in 
the diatoms. In the series taken at station 1 on September 9, 1929, and that at 
station 3 on September 11, 1929, the average number of nauplii, rotifers, and diatoms 
was somewhat smaller down to a depth of 50 meters in the former than in the latter 
series, but the reverse was true of the green algae. A comparison of the average 
numbers in the series taken at station 2 on July 21, 1927, and on July 13 and Sep- 
tember 7, 1929, with those from station 3 on July 19, 1927, and on July 9 and Sep- 
tember 11, 1929, shows that the most marked differences are represented in the dia- 
toms; even the maximum difference in this group is only a fourfold one. 
THUMB LAKE 
Five sets of net catches were secured from Thumb Lake in 1927 and two in each 
of the other three years, making a total of 11 series. (See Table 12.) The Cladocera 
were more abundant in Thumb Lake than in the upper 10 meters of Karluk Lake. 
A maximum of 263 Bosmina per liter was noted in the upper 5 meters of Thumb 
Lake on August 12, 1927 ; this form seems to have been concentrated in the upper 
stratum at this time, since the 5-10-meter stratum showed only 6.5 individuals per 
liter. On the other hand, a larger number was found in the 5-10-meter stratum 
(121 individuals per liter) than in the upper 5 meters (82 per liter) on September 7, 
1929. Again on September 6, 1930, a larger number of Bosmina was found in the 
upper 5 meters than in the 5-10-meter stratum. The maximum number of Daphnia 
(10 per liter) was obtained in the upper 5 meters on August 26, 1927. 
A maximum of 92 Cyclops per liter was noted in the 5-8-meter stratum on July 
13, 1930. Relatively small numbers of Diaptomus were obtained in Thumb Lake; 
the maximum was 3 per liter in the upper 3 meters on September 3, 1928. An un- 
usually large number of nauplii was noted in the 5-8 meter stratum on July 13, 1930, 
namely 968 per liter; the next highest was 202 per liter on July 9, 1928. 
The zooplankton of Thumb Lake was characterized by the large number of roti- 
fers. The maximum was found on September 6, 1930, when the average from sur- 
face to 8 meters was more than 3,600 per liter. The smallest number of rotifers was 
obtained in the catches of 1928; on July 9 the average number was 87 per liter and on 
September 3 it was 78. 
Protozoa were most abundant in Thumb Lake on July 13, 1930, when the aver- 
age number was 157,400 per liter of water. 
