OXYGEN SUPPLY OF CERTAIN ANIMALS 301 



Chironomid larvae^ live and are active in Lake Mendota 

 in the mud at depths where there is no free oxygen throughout 

 the summer stagnation period. This has been shown in two 

 different ways. 1) When water and mud were pumped up from 

 the stagnated region into bottles without contact with the air, 

 several times chironomid larvae were also pumped up. (Appen- 

 dix, p. 317). These bottles were tightly stoppered and set 

 aside for observation. Control bottles without larvae were 

 tested for the presence of oxygen, and none was found. For 

 methods employed, see Appendix, p. 317. Observations were 

 continued daily, and it was found that the larvae were con- 

 tinually active and lived for varying periods of time — one for 

 fifty days — death presumably being due to the accumulation of 

 waste products in the necessarily small container in which they 

 were confined. 2) Chironomid larvae obtained from the stag- 

 nated region were confined in water which had been made arti- 

 ficially oxygen-free by prolonged boiling in the apparatus shown 

 in figure 1, and described on page 318. These were active 

 throughout their life in the flask — a period varying from one to 

 three weeks. 



The difference of longevity of the larvae in "naturaP and 'arti- 

 ficial' oxygen-free water is probably due to the fact that the 

 normal chemical content of the lake water and mud (which was 

 put in every bottle to serve as food for the larvae) was disturbed 

 in the process of boiling Boiling certainly altered the character 

 of the available food. The accumulation of waste products in 

 each case was probably the immediate cause of death, as on 

 opening the bottles the odors given off were exceedingly foul 

 and smelled strongly of hydrogen sulphide. Additional support 

 for this view comes from the fact that chironomid larvae used as 

 controls in connection with the experiment just described were 

 placed in bottles of well-oxygenated surface water, and it was 

 found that they did not live appreciably longer and in some cases 

 not as long as the larvae confined in oxygen-free water. 



^ Unless otherwise stated, 'chironomid larvae' when relating to the writer's 

 experiments always refers to Chironomus tentans Fabr. 



