Summary. 



The subject under investigation has been the respiratory mechanism of the 

 Tubificidœ. The animals employed for experimental purposes have chiefly been 

 the Tubifex Rivulorum Lamarck and Limnodrilus Hoffmeisteri Claparède. Other 

 animals that I have preliminarily had under examination will be mentioned in the 

 course of the summary. 



I. General (Ecological Character of the Tubificidœ. 



A. They feed on débris. 



B. They construct tubes. 



1) With violent wriggling movements they press that part of their posterior 

 segments (which part I shall henceforth refer to as tail) projecting above the mud 

 against the surface of the latter, and in this way a mass of mud-particles is smeared 

 firmly about the tail by means of a muciuoid secretion. 



2) Simultaneously, these particles are cast off in the form of a funnel at the 

 mouth of the burrow, by the action of the animal in slowly drawing itself down 

 into the latter. 



C. They indicate the presence of saprobiotic habitat, in which they are to 

 be found in great numbers : — 



1) When the nutritive conditions are favourable, i. e. rich sedimentation of 

 organic products. 



2) And Oxygen present in fair quantities for at least rather long periods. 



3) These two phases stand in a certain state of opposition, and consequently, 

 in an adaptive respect, the Tubificidœ have to strike a balance between, on the 

 one hand, ample nutrition and at best periodical lack of 0 2 , on the other hand, 

 poor nutrition and constant abundance of O r With respect to this balancing problem, 

 the conditions must be different for various chemically and physically different 

 types of water (oligotrophia eutrophic, heterotrophic, dystrophic waters, lakes, rivers, 

 ponds, etc.). 



D. They are to be denoted as a-mesosaprobic organisms, in view of the 

 fact that the cecological spectra (Naumann 1919 a) in eutrophic water are projected 



