SURVEY OF INVERTEBRATES 43 



oxygen in concentrations varying from 9.15 to 45 per 

 cent of saturation. The organisms avoided water con- 

 taining oxygen in amounts greater than 60 per cent sat- 

 uration and occurred in small numbers in zones con- 

 taining no free oxygen at all. This last observation demon- 

 strates definitely that Loxodes is able to lead an anaerobic 

 life. The significance of the other figures is not quite 

 clear. One might be tempted to interpret them as indi- 

 cating a toxicity of oxygen at moderate tensions, but, as 

 will be seen below, such an assumption would be prema- 

 ture without further evidence. As long as the relation- 

 ship of the oxygen consumption of Loxodes to the ten- 

 sion has not been investigated, it is hardly possible to 

 draw any definite conclusions as to the type of metabo- 

 lism prevailing in these ciliates at those oxygen ten- 

 sions which they seek by preference. In view of the small 

 size of Loxodes, one would a priori be inclined to assume 

 that they could get sufficient oxygen for a purely aerobic 

 life even at relatively low tensions. The experiments of 

 Galadziev and Malm (1929) on marine protozoa con- 

 firm this view. According to these investigators the 

 oxygen tension has no marked influence upon protozoa. 

 Lund (1918), Amber son (1928) and Adolph (1929) also 

 found the oxygen consumption of Paramaecium and Col- 

 poda to be independent of the tension. In Spirostomum, 

 on the other hand, the situation is different. The respir- 

 ation of this ciliate is clearly dependent on the oxygen 

 tension, as Specht (1935) has proven. 



The interpretation of such observations as those of 

 Rylov requires great caution. Piitter (1904) noted that 

 Spirostomum dies when kept in shallow dishes and he 

 concluded that oxygen was toxic for this ciliate. Saun- 

 ders .(1924), however, showed convincingly that this con- 

 clusion was faulty and he explains the death of Spirosto- 

 mum, in Piitter 's experiments, by a change in the pH 

 of the culture water. When the latter is in contact with 

 air its pH may reach 8.0, a value which is indeed lethal. 



