THOMPSON: METAMORPHOSES OF HERMIT CRAB. 185 
The curve for these experiments would have a very limited range 
and show the mode on the fifth day. 
Series E. 
/Smistral. 
The larvae were provided with small sinistral shells and given 
opportunity to take them at will. The shells of the fresh-water 
snail, Physa heterostropha , were used. Eight experiments, using 
146 glaucothoe, 58 of which attained the moult to the sixth stage. 
No mid-period examination. 
3 glaucothoe 5 percent remained in stage 4 days. 
35 
a 
60 
u 
ll 
ll 
It 
5 
ii 
12 
ll 
20.7 
ll 
ll 
ll 
ll 
6 
ii 
8 
a 
13.8 
ll 
ll 
ll 
It 
7 
it 
The curve which may be plotted for this series is similar to the 
curves for A, B, or D except that the percentage for the sixth day is 
slightly higher (pi. 7, fig. 33, broken line). But this may be 
attributed to the fact that a large number of larvae, 36 percent, 
delayed their entrance into the shell and so retarded their develop¬ 
ment. The absence of a mid-period examination probably also 
contributes to increase the percentages for the sixth day. 
These six series of experiments clearly show that the minimum 
duration of the glaucothoe stage and phase under any condition is 
four days, and the maximum duration is eight days. In all classes of 
experiments, except those of the “ indifferent ” and “ delayed” series, 
some larvae remained in the stage the minimum period. The 
maximum period was reached not only in the “naked” but also in 
the “normal” series. The experiments also show that the shell 
exercises an influence on the rate of development proportional to 
the time which elapses between the moult from the last zoea 
stage and the time when the glaucothoe enters the shell. The 
experiments with shells of other than dextral coil, however, so 
closely resembled the latter “normal” experiments that no attempt 
was made to repeat them under “delay”" conditions. They indicate 
that the influence of the shell is independent of its form as far as any 
