PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 4 NOVEMBER 15. 1918 Number 1 1 
THE 'HOMING HABITS' OF THE PULMONATE MOLLUSK 
ONCHIDIUM 1 
By Leslie B. Arey and W. J. Crozier 
Bermuda Biological Station for Research, Dyer Island, Bermuda 
Communicated by E. L. Mark, September 18, 1918 
For some time it has been known that the limpets and their allies living on 
shore rocks exposed by the falling tide exhibit the habit of returning, on the 
approach of the period of low water, to particular spots where they have indi- 
vidually made 'homes,' slight depressions in the rock-surface, which usually fit 
with considerable exactness the form and irregularities of the limpet's shell. 
From this 'home' the limpet may creep away 50 to 90 cm., when covered by 
the sea, to feed — frequently following well-defined paths, to which it also ad- 
heres when creeping homeward again. Such experimental work as has been 
directed to the study of this peculiarity has gone to show that it may be re- 
garded as depending upon tactile and perhaps other forms of irritability (Bohn, 
Pieron), the mollusk remembering (possibly) a sensory map of the topography 
of its home region. It cannot be said, however, that this matter is as yet 
thoroughly understood. 'Homing' behavior of a similar sort has also at vari- 
ous times been attributed, in an anecdotal way, to different terrestrial 
slugs and snails. 
It seems previously to have escaped attention that homing movements of a 
more striking character are to be found in another gastropod, the intertidal 
naked pulmonate Onchidium. We have studied in this respect the behavior of 
Onchidium (Onchidella) floridanum Dall, and although further investigation 
of the subject has been planned, it is thought well to record here the nature of 
certain of our findings. 2 
The homing phenomenon to which we refer may be characterized as fol- 
lows: Onchidium lives in groups, or communities, numbering up to a dozen or 
more individuals in each, which during high tide find shelter in cavities within 
the eroded shore rock; these cavities are either narrow crevices, or may be sub- 
spherical with a diameter as great as 6 cm. ; but in any case they communi- 
cate with the exterior by means of a small and almost undetectable opening 
319 
