262 Comparative Animal Physiology 



Regulation of Breathing in Tubifex. The responses of this small bottom- 

 dwelling, fresh-water oligochaete worm constitute an interesting respiratory 

 pattern/'' •'^'* These worms have become adapted to an oxygen microstratum 

 just above the layer of mud in which they ordinarily reside. Depletion of the 

 oxygen by bacterial oxidation in the ooze below causes the worms to extend 

 themseh'es 10 or 12 times their former length to reach a satisfactory oxygen 

 zone. The extension is accompanied by rhythmic corkscrew movements which 

 agitate the water and probably draw down water containing more oxygen. The 

 respiratory movements are stimulated by oxygen lack and in intensity are 

 inversely proportional to the oxygen supply below surface. Carbon dioxide 



VESPA 





sec. 



SCHISTOCERCA 



4 sec. 



Fig. 61. Breathing movements of the wasp, Vespa orientalis, and the orthopteran, 

 Schistocerca gregaria, during flight. Arrows indicate the beginning (l) and end (i) of 

 flight movements. From Fraenkel."^ 



increase does not stimulate the movements but may in fact suspend the rhythm 

 initiated by oxygen lack. 



Ventilation Mechanisms in Polychaete Worms, An extensive study of the 

 respiratory mechanisms among polychaetes has been made by Lindroth.--'' 

 Methods of ventilation for thirty families of these worms were correlated with 

 the phyk)genetic and ecological position of the organisms. Ciliary mechanisms 

 are generally found throughout the group, concentrated most frequently on 

 the head and parapodia. Primitive errant types show undulatory movements; 

 more advanced sedentary groups have compression-type waves. The respiratory 

 currents stream backward in the lower forms and forward in the advanced 



