NATURAL HISTORY OF ONCHIDIUM 497 
intelligence' be valid for cephalopods (v. Uexkiill, '01; Poli- 
manti, '10), it is legitimate to inquire if anything of this nature 
can be imputed to Onchidium. According to Miss Thompson 
('17), the snail Physagyrina, although in maze experiments it 
gives no evidence of learning, does exhibit the establishment of 
simple associations when tested by Pavloff's method of 'con- 
ditioned responses.' There is no real evidence favoring the 
idea of memory as evinced in the 'homing' of O. floridanum. 
One adequate test of the conceivable action of associations or 
even of primitive intelligence has occurred to us. When an 
Onchidium is picked up and put down on a strange portion of 
the shore, it cannot, of course, find its old nest; but other nests 
and various unoccupied crannies are available for shelter. The 
fact is, however, that instead of seeking the shelter afforded by 
'strange' crevices, the snail is on the contrary at the mercy of 
two chief modes of response: its negative phototropism audits 
withdrawing reaction when shaded; that specific quality of its 
own particular nest which probably determines homing makes 
it possible for the creature to enter its own nest notwithstanding 
its photic sensitivities. Strayed Onchidia do not find shelter in 
new cavities of the rock, but on the contrary creep about on the 
shore until covered and washed off by the returning tide. Evi- 
dence of intelligence or of adaptive use of associative memory is 
completely absent, although, as we have elsewhere remarked 
(Arey and Crozier, '18), the close simulation of behavior of that 
order is certainly deceptive. 
SUMMARY 
Onchidium (Onchidella) floridanum is a small naked pulmo- 
nate inhabiting the intertidal shore zone at Bermuda. The indi- 
viduals of this species are grouped together into colonies num- 
bering about a dozen individuals, more or less, in each. A 
colony during high water occupies a 'nest,' in the form of an 
eroded cavity in the shore rock or a cleft between clay-cemented 
stones. During the day-time only, and at most but once in the 
twenty-four hours, the Onchidia emerge from their nest after the 
falling tide has left it above water for about an hour. The 
animals feed for a fixed period of about one hour, then those 
