Die respiratorischen Mechanismen der Tubificiden 167 



a) Id the apnœal stage, the animal follows the layer, immediately, by length- 

 reactions. 



b) In the eupnceal stage, the animal follows the layer in question, mediately, 

 by rhythmic movements and length-reactions, by which means water is pumped 

 down out of the layer. How the effect of the pumping movements rises under 

 declining 0 2 concentration is demonstrated by the curve representing the displacement. 



c) The compensatory reactions coinciding with the transition from apnœa to 

 eupncea indicate that the length-reactions are passing over from the direct to the 

 indirect category. 



d) When the respiratory layer is wandering beyond reach, maximum dyspnoea 

 commeuces. 



e) The cessation in the absorption of food denotes enterorespiratory dyspnoea, 

 which arises because the animal has difficulty in following by its reactions the 

 desired layer, when the latter rises, and instead adjusts itself to a layer poorer in 0.,. 



f) The strongly deflected course of the apncea-eupnoea-dyspnoea curve is due 

 to its congruity with the curve for the ascent of the respiratory layer under different 

 general 0 2 concentrations. 



g) The fall from maximum dyspnoea to asphyxia supervenes when the layer 

 wanders beyond reach. 



h) After the layer has wandered beyond reach, the animal does not respond 

 any longer to any fluctuations in the concentration of 0 2 , since such do not 

 subsequently occur in the »bottom- water», or in any case are exceedingly small in 

 extent. 



i) The apncea-eupncea-dyspncea curve denotes the utilisation of the micro- 

 layers at hand by the aërobically active respiratory mechanism. The break between 

 maximum dyspnoea and asphyxia indicates that, on account of the transition of 

 the respiratory micro-layer to macro-layer, the aerobic mechanism in this moment 

 ceases to function and is replaced by passive anaerobiosis (Emergent Anaërobi- 

 osis). The curve of the asphyxiai stage signifies that the passive mechanism acts 

 incessantly on account of the presence of the macro-layer. 



2) That the enterorespiratory apparatus is the central respiratory mechanism 

 for the supply of 0 2 , while in this respect cutaneous respiration plays a subor- 

 dinate part. 



a) Firstly, on account of the reasons that speak in favour of intestinal respiration, 

 enumerated under H 1), and, further, for the following reasons: — 



b) That the small caliber of the animal has no decisive bearing whatever in 

 fa vour of cutaneous respiration, at all events in the explanation of the changes 

 in length appertaining to the apnœal stage. On account of the altered layer-forma- 

 tions of 0 2 , the animal does not come into contact with a greater volume of 0 2 

 when it is distended at greatest length than when it projects up only 0-5 mm. On 

 the other hand, also in this respect, the changes in length may be interpreted to 

 signify that the animal is following a respiratory layer. 



