Die respiratorischen Mechanismen der Tubificiden 



163 



d) Possibly the defecation, the water taken in being conveyed out again by 

 this act. 



B. To changes in the percentage of 0 2 , effected by the water-change method, 

 in applying which I continually proceeded from a higher to a lower 0 2 percen- 

 tage, the Tubificidce responded by: — 



1) Fluctuations in the frequency of the rhythm: — 



a) At the highest concentrations of 0 2 , this — 0 (apncea). 



b) At a lower percentage of 0 2 varying for different individuals (14'6 — 2 - s 

 c. c. of 0 2 per litre), it rises at once from this value 0 to a rather high figure, 

 the animals being now in a normal rhythmical state, or eupncea. 



c) On a further sinking of the 0 2 teusions, the frequency rises to a dyspnceal 

 maximum. 



d) On a further diminution of the percentage of 0 2 , the frequency sinks in 

 the Limnodrilus, generally at once, from its highest value to 0. This fall between 

 maximum dyspnoea and immobility occurs simultaneously in all individuals in the same 

 experiment. By comparing the results of all my experiments in that connection, I have 

 found the corresponding percentage of 0 2 to be O'os c. c, or somewhat higher, per litre. 



e) After this fall has taken place, the Limnodrilus is rhythmically immobile 

 (asphyxia) under an unaltered or decreasing percentage of 0 2 . 



f) The above-mentioned series of reactions in the frequency apply to Limno- 

 drilus. On the other hand, the Tubifex exhibits from and including stage c), though 

 not in all individuals simultaneously, an indomitable migratory impulse that results 

 in the so-called Dyspnœal-asphyxial Migration. This migration continues even 

 in the complete absence of 0 2 , the animal moving itself freely above the mud and 

 exhibiting no respiratory rhythm. 



g) If the fluctuations in the rhythm are graphically expressed in the form of 

 a curve with the percentage of 0 2 as abscissa, this curve, though irregular, 

 shows a pronounced rise to the maximal dyspnceal stage, from which it instan- 

 taneously plunges down to 0 when asphyxia supervenes. In experiments 

 conducted in accordance with the method known as »Altwerden des Wassers» 

 (KuiPER 1907), in the corresponding curves of which the time forms the abscissa 

 and which, also in other respects, cannot be compared off-hand, the curve repre- 

 senting the rise of the frequency is, however, very regular. 



2) By variations in the length of the tail that is extended above the mud. 



a) At times of maximum 0 2 tensions (26'2 c. c. per litre) this projecting 

 portion is very little, often 0'5 mm., in order to increase gradually until the 

 termination of the apnreal stage. 



b) When the rhythm commences, the length shows a diminution — a compensa- 

 tory phenomenon between length and rhythm. 



c) Following upon this compensatory reaction, there is a gradual increase of 

 the length. 



