IOWA ACADEMY OP SCIENCES 
275 
lu addition to the material listed there were very many fra'gmeats ol’ 
vegetation so minute no attempt was made to count them. The vegetable 
material was yet sufficiently preserved that the cells could be readily seen. 
By measurement the quantity of material removed from the water by the 
net was 154 C. C. per cubic meter. Of this 138.60 C. C. or 90 per cent 
was sand and clay leaving 15.40 C. C. or 10 per cent of organic material. 
This estimate is to be considered as very conservative for the reasons 
assigned previously. 
The season up to that date June 20, 1902, had not been one of heavy 
rains to wash in large quantities of debris, but on the contrary had been 
one with moderate rains so that the quantity of vegetable material in the 
water of the cave at that date could not have been above an average for 
the summer season but was probably somewhat below it. 
The Gammarus fasciatus found in the cave seem to be normal individ- 
uals of the species with the exception of the eyes in wffiich an atrophy 
of the lens has begun although the optic lobes and nerves are yet well 
developed. These seem to be largely or wholly vegetable feeders living 
upon fragments of phaenogomous plants, and probably pass their exist- 
ence in the darkness of the cave as evidenced by beginning atrophy of 
the eye. A few individuals of Gaecidotaea were found also in the same 
cave. 
Whatever may hare been the food of the species from wffiich 
Grangonyx mucronatus was derived it became necessary as the species 
found its way into subterranean channels for its food to be largely ani- 
mal, or of vegetable debris. Some vegetation could be carried by the 
same stream that carried the crustacean but the vegetation could not 
accommodate itself to the changed conditions while the animal could. 
The crustacean would have a relatively limited supply of dead and decay- 
ing vegetable matter in addition to the other animal forms finding their 
way into underground channels. The food of G. mucronatus in those 
specimens examined consists of both animal and vegetable tissues, the 
animal supply predominating and consisting largely of Gyclops. Exam- 
ination of a few freshly caught specimens from a well showed the fol- 
lowing food materials had been taken. 
Vegetable, Algae, Drapernaldia, Gleocapsa, Oscillaria: 
Vegetable, Phaenerograms; fragments, and plant hairs. 
Animal, Earthworm fragments as indicated by setae, Rotifer eggs 
fragments of unknown Entomostraca, fragments of Gyclops. 
Specimens in an aquarium were observed seizing upon a dead Asellus 
and devouring considerable quantities. 
Plankton examinations of the wells show that only very limited 
quantities of vegetation are available as a food supply. It is ‘upon the 
animal life then that the species must largely depend for its supply, and 
this is of necessity limited in quantity. As a result of such a limitation 
a change in the number of young produced as well as in the size of the 
eggs has been brought about. There is not sufficient food for a large 
number of individuals and the struggle between these individuals is 
