298 ARCH E. COLE 



lived for forty-eight hours and one for nearly five days. Two 

 pupated during the experiment. Pause ('18) saw an error in 

 Main and Hammond's work, in the fact that the boiled water 

 might have contained small amounts of oxygen, so he con- 

 structed an apparatus similar to figure 1, page 302, in which 

 he was able to determine the amount of oxygen dissolved in 

 the water before and after each experiment. He kept the 

 larvae of Chironomus gregarius in oxygen-free water for fifty- 

 four hours. He found that the period of time during which the 

 larvae were able to survive in the absence of oxygen varied 

 directly with the amount of haemoglobin contained in the blood — 

 ,the younger the larvae, the less haemoglobin and the more depend 

 ence upon free oxygen. He concluded, however, with Maill 

 and Hammond ('00) that chironomid larvae were probably able 

 to live without free oxygen by virtue of the fact that the haemo- 

 globin could store up a sufficient supply to tide them over until 

 oxygen was again available. This point will be discussed later. 

 It is a w^ell-demonstrated fact that certain animals carry on 

 an active existence at the bottom of Lake Mendota for con- 

 siderable periods of time, living in water without detectable 

 oxygen. There is no satisfactory explanation as to how this 

 may be accomplished. This paper attempts to explain the 

 possibe sources of oxygen supply for these forms. 



PHYSIOLOGY OF THE LARVA OF CHIRONOMUS TENTANS IN 



OXYGEN-FREE ENVIRONMENTS IN LAKE MENDOTA, AND 



THEORIES RELATING TO THE SOURCE OF ITS ENERGY 



The greater part of the experimental work presented in this 

 paper was done on the larvae of Chironomus tentans Fabricius, 

 chiefly because of their size and abundance. Of the many species 

 of the genus Chironomus occurring in Lake Mendota, the larvae 

 of C. tentans are relatively abundant in the mud of the deeper 

 parts of the lake, an average of over a hundred full-grown larvae 

 being found per square meter at a depth of eighteen meters. 

 For the methods used in obtaining larvae see Appendix, page 318. 



The full-grown larvae are about 20 to 25 mm. in length and 

 3 mm. in diameter. They live in the mud at the bottom of the 



