Die respiratorischen Mechanismen der Tubiflciden 



165 



of the 0 2 -free water, the animals exhibit a fundamentally homologous, though in- 

 verted, curve. This demonstrates: — 



1) That the respiratory curve is determined reflexively solely by the 0 2 

 present. 



2) That in its essentials this curve is not determined by non-reflexive patho- 

 logical changes, which should have been produced by the fact that in the series 

 in which I have proceeded from a higher to a lower concentration of 0 2 , the animals 

 had to remain too long in water loaded with anaerobic poisons. 



E. The question of the mutual relationship between the various parts of the 

 respiratory mechanism must now be considered. 



1) The preliminary questions bearing upon this aspect of the subject have 

 reference to whether, with respect to the satisfying of the need of the Tubificidce 

 for 0 2 , we have to reckon with: — 



a) Solely intestinal respiration, 



b) Solely cutaneous respiration, 



c) Or, both simultaneously. 



2) The importance of intestinal respiration is supported by the following 

 evidence: — 



a) The internal anatomical structure, since the vascular system of the intestine 

 in the Tubifex meets the requirements of the respiratory function. 



b) The fact that the capillary net of the body-wall in the Tubificidce, except 

 for certain aberrant forms furnished with gills, is little developed, a circumstance 

 that argues against cutaneous respiration. 



c) The reactions of the animals against apneea, for it cannot be supposed 

 that cutaneous respiration can have any effect in view of the fact that the animal 

 has exposed only a zone of O b mm. of its tail. 



d) The funnel-like prolongations up into the water of the burrows. These pro- 

 longations must, of course, hamper a cutaneous respiration. 



e) That the animals live in narrow tunnels that do not permit of being flushed 

 through with water, a fact that tends to show that the respiratory mechanism is to 

 be placed as distally as possible. 



3) The evidence in favour of cutaueous respiration is as follows : — 



a) The small caliber of the animal. 



b) The water-current that is produced by the rhythm and which sweeps over 

 the body. 



c) The considerable length-reactions in the respiratory curve. 



4) A comparison of the facts adduced in paragraphs 2 and 3 prompts one 

 to assume that intestinal respiration is always active, but that when eupncea and 

 especially dyspncea supervene, cutaneous respiration acquires a growing importance 

 for the support of intestinal respiration, the latter experiencing more and more 

 difficulty in satisfying the need for 0 2 on account of the increasing deficiency of 

 oxygen. 



