Die respiratorischen Mechanismen der Tubificiden 161 



ß) The whole volume of water, regarded as a whole, is altered with respect 

 to the œcological factors. 



III. Respiratory adaptations, primarily directed against the instability. 



A. I should desire to designate some of these adaptations as active, inasmuch 

 as thanks to them the animal is able to utilise the medium immediately, despite 

 the peculiarities of the latter. They are : — 



1) That the Tubificidce are aerobic organisms requiring for vital purposes a 

 very low actively utilisable minimum of 0 2 (Great active adaptive latitude). 



2) That the Tubifieidœ have haemoglobin, which, for organisms in general, 

 does not indicate the need for 0 2 , but the difficulty of satisfying an aerobic 

 respiration. 



3) That in order to meet the fluctuations, as the latter manifest themselves 

 locally (the respiratory micro-layers) and temporarily (transitions between micro- 

 and macro-layer), the Tubifieidœ are equipped with special, aërobically active, respira- 

 tory mechanism. 



B. I should desire to designate some other adaptations to resist instability 

 as passive, inasmuch as they enable the animal to survive conditions that it cannot 

 immediately utilise, the adaptations in question being: — 



1) Great resistance to 0 2 conditions below the minimum (manifested in respira- 

 tory macro-layers) that it cannot immediately utilise. It is no longer the concentration 

 of 0 2 , but the time that is to be considered as variable. The Tubifex is capable 

 of enduring a complete lack of 0 2 for a period of 600 hours under experimental 

 conditions, and in uature assumably still more. The resistance of the Chironomid- 

 larvse was less (80 hours). This resistance appears as an anaërobiosis, without 

 the animal being able at the same time to avail itself of nutrition (Emergent 

 Anaërobiosis). 



2) Great resistance to products of anaerobic destruction and CO.,, both con- 

 centration and time constituting variables to be taken iuto consideration. The 

 Tubificidce resist C0 2 more than 24 hours at a concentration of almost 500 c. c. 

 C0 2 per litre. In fact, I never found any concentration of C0 2 that was lethal. 



C. Relating to the relationship between, on the one hand, narrow active adaptive 

 latitude and weak resistance, and, on the other hand, wide active adaptive latitude 

 and strongly developed resistance: — 



1) (Ecologically, this can be explained, for unstable (a-mesosaprobic) media 

 demand a low active minimum for existence, the percentage of 0 2 often being 

 low, and great passive resistance to lack of 0 2 and anaerobic poisons, as in these 

 media the percentage of 0 2 is often too low and only under these conditions can 

 anaerobic poisons be produced. Such variations in the percentage of 0 2 are incon- 

 ceivable in stable media. 



2) Physiologically, on the other hand, it has not been possible to demonstrate 

 any connection. The haemoglobin has here little or no significance. In the Tubifex 



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