Fig. 9. The overcrowding effect is not caused by the physical lack of space. (A) When snails (N=18) were exposed to crowding with clean shells for 24h prior to the memory augmentation procedure, LTM forms (^*P<0.05). This was determined with the use of a Wilcoxon matched-pairs signed ranks test, which showed that the number of pneumostome openings significantly decreases in the MT compared with the TS. (B) As in A, except that in addition to clean shells we added crowded pond water (CPW) as in Fig. 8. The data were subjected to a paired t-test (t=2.391; ^*P<0.02) and show that LTM is formed despite the snails being exposed to CPW and clean snail shells.