THE PLANKTON OF SHAWNEE CAVE. 393 



Amount of the Plankton.- -The amount of plankton is small 

 when compared with the amount taken in a lake or epigean stream. 

 In low stages, 200 gallons contained less than i c.c. In times of 

 flood the catch was increased very much (200 c.c. or 300 c.c.), 

 but this increase was largely due to silt and vegetable debris 

 carried in suspension. 



Constituents of the Plankton. No organisms were found that 

 were not referable to known epigean forms. Rather marked 

 variations from the type were observed in some of the Crustacea, 

 notably in the genus Bosmina. However, the recent work of 

 Wesenberg-Lund makes it advisable to withhold judgment on 

 this point, until the local and seasonal variations in the Crustacea 

 of the ponds of the region have been investigated. 



The zooplanktonts taken included Copepoda, Cladocera, Roti- 

 fera and Protozoa. 



The phytoplanktonts belonged to the following genera : Spiro- 

 gyra, Zygnema, Volvox, Closterium, Micriasteria, Vaucheria and 

 Pandorina. In addition to these, diatoms, worms, insect larvae 

 and fragments of spiders occurred rarely. 



The planktonts having the widest temporal distribution were 

 Bosmina cor nut a, Cyclops biciispidatus and Anura cochlearis. 

 Cyclops prasinus outnumbered Cyclops bicuspidatus in November 

 and several species of Rotifera were quite common in May. 



The loricum probably enables rotifers to withstand cave condi- 

 tions as all the Rotifera except two belong to the suborder 

 Loricata. These two were found when the current was quite 

 rapid and disappeared when the water became low and the cur- 

 rent reduced. There may be other factors in the organization of 

 the Loricata besides the loricum that enables them to exist under 

 these conditions. That the rotifer fauna of the cave is included 

 with rare exceptions in this subclass is certainly significant. 



Diatoms were very rare. This was probably due to two 

 things (l) these forms live on the bottom of the ponds and 

 consequently few are carried into the cave, (2) they soon succumb 

 in the cave. 



Other algae were never taken in large quantity, but Volvox 

 and Closterium were present in most of the catches throughout 

 the year. Filamentous algae were found at Shawnee Cave only 

 in the higher stages of the stream. 



