439 
Vautre.” It is evident that this can occur only when similar conditions (e. 
g., pelagic) are present in the different lakes. In lakes this similarity may 
exist in certain parts during the major part of their existence. In ponds 
the peried for this reciprocal reaction is very limited. 
Although a single pond contains relatively few species, all the ponds 
in an avea of several square miles show a much greater variety. 
Many ponds have been examined but detailed data concerning them 
have not yet been collected. However, the following note will illustrate 
what is meant. On Jan. 11, 1910, pond No. 1 P contained Cyclops bicuspi- 
datus, Chydorus sphaericus, Cypridopsis vidua and alona. Pond No, 2 T 
contained Cyclops serrulatus, C. leuckarti; and an unidentified Daphnid. 
Pond No. 6 P contained a few Cyclops serrulatus and an enormous number 
of Bosmina cornuta. Other groups of organisms show an equal variety. 
RELATION TO CAVE PLANKTON. 
This variety in the fauna of different ponds has an important bearing 
upon the relation of pond plankton to that of caves. That the plankton 
of the cave streams of this region is derived from certain of these ponds 
is well established. Only a small number of the organisms in any pond 
are able to withstand the inimical cave conditions. I have never found all 
the species reported from the Shawnee Cave stream in any one pond. 
These facts indicate that the cave plankton is a composite of such or- 
ganisms of the contributing ponds as are able to withstand cave condi- 
tions. It is probable that the greater the number of contributing ponds, 
the richer will be the fauna at the outlet of the cave stream. 
The relation of these solution ponds to a cave stream is quite com- 
parable to the relation of backwater lakes, bayous, oxbow cutoffs, ete., to 
the river in whose valley they lie. WKofoid (’03, p. 546) states concerning 
the Illinois River, “The plankton indigenous to the channel itself is of 
small volume as compared with that contributed from the backwaters.” 
There is, however, this difference. In the cave the processes of growth 
and reproduction are very much inhibited, while in the river they continue 
or may even be increased. Kofoid (lc) has shown that during periods of 
low water, the river may contain more plankton than the contributing 
waters. This condition never exists in cave streams and obviously never 
can exist. 
