Oct., 1920 Bulletin of the Brooklyn Entomological Society 91 



body {e.g., Odonata larv«, Chironomid larvae) ; and external oxy- 

 genation, i.e., the oxygen exchange takes place outside of the body 

 {e.g., adult beetles). 



2. General Physiology of Respiration. 



The principle involved is that of a diffusion of gases through a 

 moist membrane. We all know that obeying the laws of gas dif- 

 fusion gases will tend to form an equilibrium on both sides of a 

 moist membrane ; or, if in solution, on both sides of a membrane 

 separating two liquids. Such is, simply put, the condition in an 

 aquatic insect. There is a certain gas pressure in the body of the 

 insect; the water around the insect contains gas in solution; a 

 membrane, the cuticle plus hypodermis, separates the two, and 

 throughout the membrane the gases tend to equilibrate. 



In aerial respiration of insects the dry atmospheric air is led 

 by the tracheae and tracheoles directly to the cells where it passes 

 into solution in the cell cytoplasm. The process is assisted by 

 inspiratory movements of abdomen and thorax and by the clos- 

 ing mechanism of the spiracles. Fundamentally, however, the 

 principle of respiration in aquatic insects is that of a gas balance 

 of two sides of a membrane. This has been definitely called a 

 diffusion theory in contradistinction to the older secretion theory. 



3. Internal Oxygenation. 



By internal oxygenation is meant that the oxygen renewal takes 

 place within the body, or at least at the surface of a membrane, 

 — much as in our own lungs, or as in the gills of fish. There are 

 two methods found in insects. Briefly, these may be called the 

 tracheal, or gaseous method, and the fixation, or solution method. 

 In the tracheal method the oxygen goes out of solution at once 

 and is carried to the tissues in gaseous form by the tracheoles. 

 In the fixation process the oxygen passes through a membrane 

 and is fixed by a respiratory pigment in the blood plasma, and 

 passes out of solution later on. 



The tracheal method has been studied very extensively among 

 insects, and primarily in the Odonata. In several excellent papers 

 Tillyard has taken up the Odonate respiration in a very thorough 

 manner, particularly that of the lantern type of rectal gills found 



