242 THE UNIVERSITY SCIENCE BULLETIN. 



C. Check. 



a. Boil some of the surveyed culture to kill organisms. 



1. Place carmine over this in stender and repeat the series under 

 B6. 



Culture 17129 was made by grinding water-soaked leaves of 

 dead Typha. These grindings had reached a state of balance 

 before using in this experiment. It had been used to rear 

 Corixids and so was known to contain the essential elements 

 of the boatman food supply. • A survey of the culture is given 

 elsewhere, but it is well to recall that it consisted of ground- 

 up bits of Typha tissue, a few Englenids, some Tetraspora, 

 some algal filaments, live and dead rotifers, about equally 

 divided, some nematode worms, and here and there various 

 protozoans. 



Some carmine was then sprinkled over a layer of this ma- 

 terial in a stender and allowed to stand for 24 hours to note the 

 effect of the carmine upon the animal organisms. The animals 

 were alive and the nematodes and rotifers and some of the pro- 

 tozoa contained carmine, not in considerable quantities, how- 

 ever. One dead Oligochseta was quite strongly stained. 



Adult Corixids of the species PalmacoHxa buenoi, after 12 

 hours in clear water, were placed on this carmine forage, and 

 began feeding at once. By the end of ten minutes the anterior 

 end of the stomach of one af them was carmine red. Besides 

 carmine grains, there were present some rotifer skins, one with 

 red in it, open jaws of rotifers, and some green Englenids, 

 Other specimens show the presence of considerable carmine 

 mixed with plant matter some algae filaments, and here and 

 there a nematode. In all, the digestive tracts were filled with 

 red matter, a little of which could be traced directly to the 

 animals consumed. The colored drawing of a nematode shows 

 one source of the carmine. 



To determine whether Corixids were after live animals or 

 would eat dead ones, too, some of the Typha was cooked. An 

 examination showed dead rotifers and worms, etc. Added car- 

 mine to this, with the idea that the animals being dead could 

 not ingest it. Corixids began foraging at once. An examina- 

 tion of their stomachs showed that they were taking up plant 

 matter and carmine grains, also some of the dead rotifers, etc. 

 After a few hours the dead animals had taken up the stain and 

 in this way would account for some of the red in the Corixids, 



