94 SURVEY OF INVERTEBRATES 



the animals have been reported to survive anaerobically 

 for long periods both under natural and under experi- 

 mental conditions. If they would obtain their oxygen 

 from the crystalline style, such a discrepancy would be 

 hard to explain. Secondly, it has been emphasized, es- 

 pecially by Maloeuf (1937), that the crystalline style is 

 such a small structure that one cannot easily conceive how 

 significant amounts of oxygen could be liberated from it. 

 Thirdly, according to Nelson (1925) and Yonge (1926a), 

 there is no correlation between the size of the lamelli- 

 branchs' crystalline style and the degree of aeration of 

 their surroundings. Finally, recent studies {e.g., Dugal, 

 1939) have directly demonstrated that even in clams that 

 are not kept under very strict anaerobic conditions true 

 anaerobiosis takes place. (This will be reviewed in de- 

 tail later.) 



Weighing the available evidence, the present writer is 

 convinced that the clams behave like other invertebrates 

 and that they do not store oxygen in amounts which are 

 large enough to exert a significant influence on the metab- 

 olism during longer periods of oxygen want. 



2. GASTROPODS 



The gastropods seem to be the first invertebrates that 

 were exposed to anoxic conditions. In his posthumous 

 work "Memorie su la respirazione" Spallanzani (1802) 

 states that he confined snails in vessels in which the air 

 had been replaced either by carbon dioxide or by hy- 

 drogen. In the former case he found a survival of less 

 than 40 hours, in the latter, a survival of at least 18 

 hours. He noticed also that snails kept in closed vessels 

 were able to consume all the oxygen present. He finally 

 gives some data on the carbon dioxide produced under 

 these circumstances. Before Spallanzani 's work appear- 

 ed, it was generally assumed, on the basis of Vauquelin's 

 experiments (1792) that snails placed in closed vessels 

 die rapidly after all the oxygen has disappeared. 



