NATURAL HISTORY OF ONCHIDIUM 495 
even when the margin of the shell had been chipped away, and 
concluded therefore that the 'topographic memory' involved 
must be a sensory affair. The deduction is reasonable that the 
cephaHc tentacles are the essential guiding organs, particularly 
in creeping, and that the pallial tentacles serve this function 
while the Patella is adjusting its irregularly outlined shell to the 
depression of the scar. But it should not be forgotten that the 
experimental test of this conclusion, particularly in so far as it 
pertains to the somewhat obscure 'topographic memory,' has 
yet to be instituted. 
With reference to the bearing of these findings upon the 
analysis of 'homing' in Onchidium, we need only point out that 
the homeward creeping of the latter has a much more flexible 
cast than is true of the behavior of the limpets, especially 
in those experiments where an Onchidium removed from one 
entrance of its nest and replaced upon the rock was found to 
gain the nest again, but by a second, different aperture. The 
distances from which a successful return is effected are also 
notably greater in the case of Onchidium. Nevertheless, the 
probability of any deep-seated 'memory' of the location of the 
nest is negatived by the fact that confinement to the laboratory 
for twenty-four hours obliterates the capacity for return to the 
nest. Tests of this point with Fissurella and Patella are of great 
interest; according to Pieron ('09 b), the abihty of Patella to 
return to a particular 'home' can survive some days' removal 
from the scene. Even bees are said to lose their memory of 
specific locations after being anaesthetised (quoted from Min- 
nich, '19). 
The behavior of limpets is of greater significance in connec- 
tion with the possible evolution of the 'homing' capacity. Some- 
thing of this sort seems to have been in Wells's ('17) mind. It 
can be pointed out that several grades of increasing precision 
and complexity of 'homing' activity are shown by molluscs 
(Arey and Crozier, '18). Beginning with Chiton tuberculatus 
(Crozier, '21), in which there can be found something hke 'hom- 
ing,' but of a rather vague type and pretty certainly the result 
of immediate stimulations, a series comprising also Patella, 
