162 



Gust. Alsterberg 



and still more clearly in the red Chironomid-\&rvs&, it undergoes under anaërobiosis, 

 like other tissues, a decomposition," which I would characterize as an Anaerobic 

 Inanition. 



D. It might have been expected that instead of this combination of active 

 and passive adaptations, the Tubificidœ would have attained an anaerobic life like 

 the intestinal parasites. That such a transition has its definite difficulties is 

 evident from an œcological and physiological standpoint: — 



1) For higher organisms, the medium is not fitted for anaerobic metabolism. 



2) Only few higher organisms in this medium can be suspected of having 

 undergone transition from aërobiosis to such a complete anaërobiosis, e. g. Gorethra- 

 larvœ, certain Cyclops. 



3) The problem of the transition from aërobiosis to so complete an anaërobiosis 

 combined with nutrition seems just to lie in the absorption of food. 



4) That, thus, the gap between the anaërobiosis combined with nutrition — 

 which I have therefore denoted as constant and which is an active adaptive form 

 — and the passive Emergent Anaërobiosis which supplements the great active 

 adaptive latitude, is far greater than what a superficial comparison seems to show. 



IV. Active Aerobic Respiratory Mechanism. 

 A. Functional Respiratory Mechanism. 



1) The rhythm of the oscillating tail. This rhythm has the following character: — 



a) It takes place in the dorso-ventral plane. 



b) It proceeds in a proximal direction. 



c) The amplitudes are at least approximately equal under different conditions 

 and in different sections of the same animal. 



d) The frequency is fairly constant under unaltered external conditions. 



e) On the other hand, the frequency is unequal in the LimnodriJus and Tubifex, 

 being under the same conditions greater in the latter genus. 



2) The length of the posterior portion, the tail, which can vary in length on 

 account of the animal drawing down into the mud or pushing up over the latter, 

 by means of contractions and expansions that affect its body as a whole, varying 

 extents of this part, 



3) The current of water, the Displacement, which has the following character: — 



a) It is produced by the rhythm. 



b) Like the oscillating waves, it proceeds in a proximal direction. 



c) It is a function of the length of the tail and the frequency of the rhythm. 

 (Formula: Displacement ~ 1 X f)- 



4. Enterorespiratory movements, which are the same in the Tubificidœ and 

 Lumbriculus, and which consist of: ■ — 



a) Non-rhythmical opening and closing movements of the anal opening. 



b) Vibratory ciliary movements in a proximal direction. 



c) Intestinal pulsations in a proximal direction. 



