SURVEY OF INVERTEBRATES 123 



pendent on the duration of the preceding anoxic pe- 

 riod (Plateau, 1872; Bruneteau, 1931; Kalmus, 1935). 

 Second, in all cases investigated, the repayment of an 

 oxygen debt, indicating the removal of oxidizable sub- 

 stances, has been observed (Gaarder, 1918; Davis and 

 Slater, 1927; Bodine, 1928; Gilmour, 1940, 1940a, 1941, 

 1941a; Harnisch 1941). 



C. Influence of low oxygen tensions. The metabolism 

 of terrestrial insects seems, on the whole, to be inde- 

 pendent of the oxygen tension within wide limits, but if 

 the tension is considerably lowered (in the case of grass- 

 hopper eggs, for example, below 25 mm. of mercury, ac- 

 cording to Bodine, 1934) a gradual replacement of aerobic 

 by anaerobic processes may be expected, as in any other 

 group. This will be discussed in greater detail later. 



A number of interesting experiments concerning the 

 influence of low oxygen tensions have been carried out 

 with Drosophila. Csik (1939) studied the sensitivity of 

 six fruit fly species, determining the minimal amounts 

 of oxygen required for maintaining motility of the im- 

 agines at the temperatures optimal for each species. He 

 arrived at values ranging from 1.6 per cent in Droso- 

 phila melanogaster to 2.8 per cent in Drosophila ohscura. 

 Kalmus (1937) found that about the same oxygen con- 

 centration (2 to 3 per cent) was required to allow the 

 pupae to develop into adults. If the pupae were exposed 

 for a period of 8 hours (Kalmus, 1935a) to a vacuum of 

 18 mm. Hg, their subsequent hatching in a normal at- 

 mosphere was retarded for almost 8 hours, which seems 

 to indicate that the development had stopped more or 

 less completely during the period of oxygen deficiency. 

 In a later paper (1937), however, Kalmus stated that in 

 longer-lasting experiments and with even stricter anaer- 

 obic conditions, indications were found that at least some 

 developmental processes went on in the absence of oxy- 

 gen. He compared the time necessary for completion 



