SURVEY OF INVERTEBRATES 95 



The more recent findings about the anaerobic survival 

 of gastropods are summarized in Table 12. They indi- 

 cate that, contrary to what has been found in lamelli- 

 branchs, there is no direct connection between the ability 

 to respire anaerobically and the possible lack of oxygen 

 in the surroundings. Alsterberg (1930) pointed out that, 

 at given temperatures, terrestrial gastropods, like Helix, 

 survive about as long as the aquatic snails Limnaea or 

 Planorbis, and almost as long as Vivipara or Bithynia. 

 He concludes that the gastropods show a certain resis- 

 tance to lack of oxygen regardless of their ecological 

 relationships. 



Alsterberg might even underestimate the anaerobic 

 functions of Helix. He immersed his specimens in water 

 containing little oxygen and determined the death time in 

 this medium. It is well known that Helix and other ter- 

 restrial snails die rather rapidly if submersed in water, 

 even when it is well aerated. This has been shown by 

 Ratfy and Fischer (1931, 1934) for Helix and Succinea 

 and by Colosi (1932) for Helix and Limax. But death 

 seems to be due primarily to an osmotic disturbance and 

 thus the true resistance of the animals to lack of oxygen 

 might have been masked in Alsterberg 's experiments. 



There are no indications that, under natural condi- 

 tions, terrestrial gastropods may have to respire anaero- 

 bically to any marked extent. The possibility, however, 

 that some anaerobic processes may go on, even at high 

 oxygen tensions, cannot be excluded, since snails, in gen- 

 eral, seem to belong to the class of animals whose oxygen 

 consumption depends to a marked degree on the tension 

 (Thunberg, 1905; Harnisch, 1932). 



Whether or not hibernating terrestrial snails ever find 

 themselves in oxygen-free surroundings has, to the pres- 

 ent writer 's knowledge, never been investigated. It seems 

 likely, however, that this maj- happen from time to time. 

 Many species burrow rather deeply into the ground and, 



