274 
IOWA ACADEMY OF SCIENCES 
vegetable debris in variable quantities at different times. Minute fresh 
water algae no doubt occur there, the spores being brought in by external 
communication, while remains of larger forms, as confervae etc. wmuld 
occur plentifully after floods.” 
In a very recent communication with reference to the feeding habits 
of cave Crustacea Prof. C. H. Eigenmann says: “I know that in our 
caves about here (Bloomington, Ind.) they depend on decaying vegeta- 
tion carried into the caves. In Cuba they live directly and indirectly on 
the roots of trees growing on the margins of the caves.” 
In the summer of 1902 in company with Mr. R. E. Richardson of the 
Illinois State Laboratory of National Historj^ I made a visit to a cave in 
Monroe Co., 111. In the vicinitj^ of the cave are many sink holes which 
probably have communication with the cave or with others near by. Oak 
leaves present in the small stream flowing through the cave indicate 
some of the openings for communication with the outer world are of 
relatively large size. In this cave numbers of individuals of Gammarus 
fosciatus were taken; an examination of the alimentary tracts of several 
specimens showed the presence of no other food than fragmentts of 
phaenogom.ous plants. In addition to the vegetable fragments there were 
grains of sand and some minute mineral crystals. A brief examination 
of the plankton of the cave by Mr. Richardson showed the presence of at 
least two species of Entomostraca, four species of Rotifera, two of 
Protozoa, four of Algae, besides quantities of vegetable debris. The col- 
lections were not taken with the idea, at the time, of making a quantita- 
tive examination so the amount of water passing through the bolting 
cloth was not measured. The estimations of the amount of plankton 
are not at all accurate but were made under rather than over the actual 
amount. A bottle of plankton was counted that was believed to repre- 
sent the amount taken from about five liters of water but in making the 
estimate it was considered to represent the quantity from ten liters. 
The usual method of precipitation and counting the plankton was fol- 
lowed, and the estimate made for one cubic meter of water. The esti- 
mate is as follows: 
J’haenogfmons vegetable fragments, length 1000 microns, 
or more 3,900,000 
riiaen^gamous vegetable fragments, length 500-1000 microns 4,230,000 
I’haenogamons vegetable fragments, length 100-500 microns 21,480,000 
Phaenogamons epidermal hairs 1,470,000 
root hairs 510,000 
Algae, Cladophora fragments 60,000 
Mesocarpus 30.000 
Spore cases 30,000 
Total vegetable 31,770,000 
i’rotozoa, A reel la discoides 90,000 
Potifera. Brachionns angnlaris 90,000 
Entomostraca, Evclons fragments 30,000 
Nanplii 120,000 
Total animal 330,000 
Total animal and plant 32,100,000 
