SURVEY OF INVERTEBRATES 67 



(c) Terrestrial forms. To what extent 

 terrestrial worms, mider natural conditions, live anaero- 

 bically is not known. There is good reason to believe that 

 they often find themselves in very difficult respiratory 

 conditions after rains. Normally, earthworms get their 

 oxygen directly from the atmosphere, but they are also 

 able to extract oxygen from water. Nagano (1934) kept 

 Eisenia foetida alive up to 94 days, and Pheretima com- 

 munissima up to 41 days, in running water, at 14° to 

 25° C and Raffy (1930) showed that earthworms im- 

 mersed in water saturated with oxygen consume the same 

 amounts of oxygen as controls kept in the air. When 

 the oxygen content in either case was lowered, the oxy- 

 gen consumption decreased, the decrease being more pro- 

 nounced in water than in air. The curves obtained by 

 various authors (Jordan and Schwarz, 1920 ; Dolk and van 

 der Paauw, 1929; Thomas, 1935) for the oxygen consump- 

 tion of earthworms in relation to the oxygen tension of 

 the atmosphere are not very uniform, but they all show 

 that, despite the presence of haemoglobin, the oxygen con- 

 sumption is considerably lower than normal at low ten- 

 sions. 



Since rain water upon entering the ground rapidly 

 loses its oxygen (Merker, 1926), it seems quite certain 

 that it is actually the danger of asphyxiation that drives 

 the worms to the surface after heavy rains (Merker, 

 1931). To what extent the metabolism of these animals 

 becomes anaerobic before they leave the ground is diffi- 

 cult to ascertain. But not all the earthworms come to 

 the surface or die in the ground after a rain, even after 

 a long-lasting rainy period ; the mere fact of the survival 

 of many suggests a quite marked ability for at least par- 

 tial transition to anaerobiosis. 



B. Resistance under experimental anaerobic conditions. 

 The data concerning the resistance of non-parasitic worms 

 experimentally deprived of oxygen have been summa- 

 rized in Table 10. It is quite apparent, on the whole, 



