PART I 



OCCURRENCE OF ANAEROBIOSIS AMONG 

 INVERTEBRATES 



Before surveying the invertebrate phyla for evidence of 

 anaerobic life we shall (1) discuss the methods of inves- 

 tigation used in this field and (2) consider the types of 

 habitats in which anaerobiosis is possible. 



CHAPTER I 



METHODS OF INVESTIGATION 



The study of anaerobic life in invertebrates comprises 

 three essential problems: 1. the presence of animals in 

 habitats in which there is a lack of oxygen ; 2. the toler- 

 ance of animals for the experimental deprivation of oxy- 

 gen; 3. the nature of the metabolism under anaerobic 

 conditions. From the standpoint of methodology the first 

 of these problems involves the technique of measuring 

 the oxygen content of various habitats; the second, that 

 of establishing experimental anaerobic conditions; and 

 the third that of determining the type of anaerobic me- 

 tabolism. These methods, although partially overlap- 

 ping, will be discussed separately. 



1. DETERMINATION OF THE OXYGEN CONTENT OF 

 VARIOUS HABITATS 



A. Terrestrial habitats. True terrestrial animals live, 

 in so far as their respiration is concerned, in a gas- 

 eous atmosphere. The oxygen content of the latter can 

 usually be determined with the help of standard gas 

 analysis apparatus. Detailed directions for the handling 

 and analysis of gases are given by Peters and van Slyke 

 (1931). In special cases it will be necessary to work with 

 small gas samples; the procedure of micro gas analysis 



