H. MUNRO FOX 569 



By this method the relative amounts of oxygen absorbed by dif- 

 ferent surfaces of a small aquatic organism can be estimated very 

 delicately. Most oxygen is taken in at those places where most 

 flagellates accumulate and where, later on, the aggregation first 

 moves away from the surface in the form of a band. The use of the 

 flagellates as an indicator in such work has the more value in that 

 they can be cultivated either in fresh or in salt water. Throughout 

 the present investigation the flagellate employed was Bodo sulcatus. 

 It was obtained by steeping grass from the garden behind the labora- 

 tory at Plymouth in tap water. 



Fig. 5. Simuliwn pupa in a suspension of flagellates. A, the flagellates col- 

 lect on the surfaces which are absorbing oxygen; B, later, the flagellates leave 

 the region where the oxygen concentration has fallen below the optimum for them. 



The use of flagellates for detecting the intake of oxygen by the 

 surfaces of organisms is complementary to Engehnann's well known 

 method of demonstrating the output of oxygen in photosynthesis by 

 means of bacteria.^ 



The flageUates have been used so far to test the respiratory activi- 

 ties of several types of aquatic insect larvas, but the work so far has 

 been done mostly from the point of view of perfecting the methods. 

 In the future it is proposed to examine systematically all available 

 types of larvae with the particular object of settling the functions of 

 the several kinds of so-called gills. To make the meaning clearer, 

 the work done with the red Chironomus larva will now be outlined. 



^ Engelmann, T. W., Neue Methode zur Untersuchung der Sauerstoffausschei- 

 dung pflanzlicher und thierischer Organismen, Arch. ges. Physiol., 1881, xxv, 285. 



