572 RESPIRATORY EXCHANGE IN AQUATIC ORGANISMS 



individual larva in the same relative amounts that oxygen is absorbed 

 by these surfaces; (4) that the "anal gills" give off no more carbon 

 dioxide than the general body surface; and (5) that the ventral gills 

 give off no carbon dioxide. 



It is intended to apply the flagellate method of studying the oxygen 

 intake and the indicator method of studying the carbon dioxide 

 output to small aquatic types of the various groups of the animal 

 kingdom, but first of all a systematic examination will be made of 

 aquatic insect larvae with special reference to the functions of the so- 

 called blood gills and tracheal gills and to the relation of closed 

 tracheal systems to respiration. 



SUMMARY. 



1 . Flagellates are positively chemotactic to a certain concentra- 

 tion of dissolved oxygen which is lower than that in water saturated 

 with oxygen under atmospheric partial pressure. Consequently, 

 when a small aquatic animal is held motionless between cover-slip 

 and slide in a suspension of flagellates in water saturated with oxygen, 

 the flagellates are attracted to those parts of the animal which are 

 absorbing oxygen. The relative sizes of the flagellate aggregations 

 then show the relative activities of the different surfaces of the animal 

 in absorbing oxygen. 



2. Applying this method to the red Chironomus larva it was found 

 that the animal respires by the whole body surface except by 

 the head and the "ventral gills" and that the relative intensity of 

 oxygen intake by the different parts of the body varies in different 

 individuals and in the same individual at different times. 



3. The absenceof oxygen intake by the"ventral gills" was confirmed 

 with the microspectroscope. In oxygen-free water all the hemo- 

 globin of the blood becomes reduced. When an air bubble is now 

 introduced so that it touches the "ventral gills" oxyhemoglobin first 

 appears in the nearest body segment to the bubble, not in the "gills." 



4. When a small aquatic animal is held motionless between cover- 

 slip and slide in a solution of an indicator which changes color about 

 the neutral point of water the relative extent of color change at dif- 

 ferent surfaces of the animal's body indicates the relative amounts 

 of carbon dioxide given off by these surfaces. 



