SURVEY OF INVERTEBRATES 103 



ganism has not, so far, been studied experimentally in 

 that respect. 



■ Interesting observations have been made on cirripeds. 

 The barnacle CJithalamus stellatus, according to Mon- 

 terosso (1932, 1932a) withstands without difficulty strict- 

 ly anaerobic conditions for periods of more than 14 

 days. Naturally, the question arises whether this sur- 

 prising resistance is of ecological significance. It is well 

 known that barnacles frequently establish themselves in 

 localities where they may not be submerged in water 

 for rather long periods. Moore (1935) remarks that Ba- 

 lanus balanoides may be exposed to air as long as a week 

 in its normal habitat. He states: "when exposed to air, 

 the barnacle's shell is closed, and the barnacle is extreme- 

 ly resistant to adverse outside conditions." As shown 

 in a previous section, clams kept in a similar fashion close 

 their valves so tightly that an anaerobic milieu becomes 

 definitely established inside the shell. Barnacles do not 

 seem to behave exactly in the same manner. Some ob- 

 servations by Monterosso (1927) indicate that in CJithal- 

 amus a minimal opening of the shell persists, and Borsuk 

 and Kreps (1929) have demonstrated that Balanus bal- 

 anoides and Balanus crenatus are actually able to con- 

 sume oxygen, though at a decreased rate, when kept out- 

 side the water. The figures given by the last-mentioned 

 authors are unfortunately insufficient to decide whether 

 the decrease in oxygen consumption is so marked as to 

 lead one to assume that there is a partial transition to 

 anaerobic life. The question is very interesting and 

 should be investigated further. 



An indication that transition to a partially anaerobic 

 metabolism is possible in cirripeds can be found in ob- 

 servations by Kreps (1929). He demonstrated that the 

 oxygen consumption of Balanus crenatus, in water, de- 

 pends to a marked degree on the salinity. In water with 

 a salt content of less than 0.6 per cent it is minimal, 

 the animals being anabiotic. The interesting point, how- 



