568 



RESPIRATORY EXCHANGE IN AQUATIC ORGANISMS 



the walls of certain filamentous appendages, no oxygen at all being 

 absorbed by the rest of the body surface, the aggregation and band 

 of flagellates have the forms shown in Fig. 5. In all cases the band 

 gradually enlarges, moving out to a stationary equilibrium position 

 just within and parallel to the edges of the cover-glass. This is the 

 same phenomenon as the final stage of spontaneous aggregation and 

 band formation. 



Fig. 3. 



Fig. 4. 



Fig. 3. The same larva a little later. The flagellates leave those surfaces of 

 the larva which by their more active respiration have first reduced the concen- 

 tration of dissolved oxygen below the optimum for the flagellates. 



Fig. 4. The same larva. The flagellates have all left the surface of the larva 

 and lie in a gradually spreading band in the zone of optimum oxygen concentration. 



