488 LESLIE B. AREY AND W. J. CROZIER 
back and forth or 'hesitation/ and even to creep within the new 
entrance. But never, in these tests, did such a snail remain in 
the strange nest. Not infrequently several journeys were made 
about the foreign opening (Arey and Crozier, '18). 
A further significant result was that in several of the tests 
made upon Onchidia taken from nests subsequently found to 
possess two apertures, the successfully homing snails gained 
entrance by way of a cleft different from that which they had 
followed in their undisturbed homeward trip. 
The specificity of the assumed 'olfactory' substance is not 
'remembered' by an Onchidium after twenty-four hours' con- 
finement to the laboratory. This point was repeatedly tested 
at Dyer Island. Such confinement obliterates the possibility of 
homing to the old nest, even from distances of a few centimeters. 
Our conception of the role of the oral lappets might be taken 
to explain the functional significance of certain curious glands 
located on these organs, in certain species. Plate ('94), with 
Oncis, and later Pelseneer ('01, p. 20), with Oncidiella patelloides, 
found on the sides of the oral lappets a pair of symmetrical aper- 
tures, the orifices of glands compared by Pelseneer to the anterior 
tentacular glands of Vaginula, but of unknown function. In 
0. fioridanum, however, these glands are not present, otherwise 
one might suggest that these peculiar organs furnish a mucous 
covering for the oral lappets, perhaps containing a material 
serving as a specific solvent for hypothecated odoriferous emana- 
tions from the nest. It would be interesting to know how 
widespread the 'homing' may be among these related species. 
This hypothesis not only accounts for all the facts known to 
us, as already stated, but obviously avoids reference to such 
obscurely defined notions as 'muscular memory' and the like. 
The hypothesis could best be tested by means of experiments 
upon the homing tendencies of Onchidia which had not been 
permitted to feed, and by the attempted discovery of the sub- 
stance naturally responsible for our 'reversal of inhibition.' It 
should be noted that we distinctly avoid saying whether or not 
such substance may be derived from' the algae ingested, because 
a certain amount of calcareous mud is also swallowed while 
feeding (Crozier and Arey, '19 a). 
