482 Wisconsin Academy of Sciences, Arts, and Letters. 
general average for all samples from the five deep-water stations. 
This quotient has been taken as the vernal crop of these two forms 
in the intermediate zone. 
The 5--7-meter region is very sparsely populated as compared 
with the areas a meter or two deeper. The averages of the 21 sam¬ 
ples obtained at a depth of 8 meters are from eight times to seventy- 
five times as large as those shown by Muttkowski for the 5—7-meter 
area. The differences are still more marked when the latter is com¬ 
pared with the data for 9 meters and 10 meters, or for greater 
depths. 
Limnodrilus and Tubifex. These two forms show a fairly regu¬ 
lar increase in numbers with the increase in depth; the average 
between 16 meters and 20 meters is about eight times as large as 
that at 8 meters. At 17 meters, however, the difference is almost 
fourteenfold, but the average for this depth is probably larger than 
it should be because three of the five samples here contained unus¬ 
ually large numbers of these Oligochaeta. The samples from sta¬ 
tion I (18.5 meters) gave substantially the same mean as those 
taken at a depth of 18 meters. The averages for station II and for 
the five deep-water stations combined are appreciably larger than 
the average for 20 meters, while the mean of all samples from the 
intermediate zone is less than half as large as that of the deep 
water zone. 
Pisidium iddkoense. The most marked increase in Pisidium in 
the intermediate zone was between 8 meters and 9 meters, the latter 
depth yielding more than twice as many as the former depth. The 
averages between 10 and 20 meters show considerable irregularity, 
but there is a general tendency for the numbers to increase some¬ 
what with depth. The largest average for this zone was found at 
19 meters. The general average for the whole zone is only a little 
more than 63 per cent, as large as that for the deep-water zone. 
Chironomus tentans. The larvae of Chironomus show a rather 
irregular increase with depth in the intermediate zone, but their 
maximum point is reached at 18 meters. Beyond this depth the 
number decreases, and the average for the whole zone is a little 
more than twice as large as that of the deep-water zone, thus show¬ 
ing a preference for the former area. 
Corethra punctipennis. This larva shows a decided preference 
for the deeper water; the general average for the intermediate zone 
is a little less than one third as large as that of the deep-water zone. 
