484 LESLIE B. AREY AND W. J. CROZIER 
of the rock. It was not possible, although several tmies the 
attempt was made, to establish an artificial tidal rhythm bj' 
periodically lowering the water level in such aquaria; this phase 
of the work will, we hope, be continued. Experiences of this 
sort plainly indicated the existence of some very specific corre- 
lation between the natural behavior of an Onchidium and the 
features of its ordinary home. 
In our opening description of the chief phases in the daily life 
of O. floridanum we have already given a brief account of the 
most remarkable aspect of this specific correlation, namely, the 
snail's 'homing' behavior. It was obviously necessary to inquire 
into the nature of this peculiar activity. Although our results 
are not in any sense exhaustive, for we were unable to complete 
the series of experiments planned, the evidence we do command 
nevertheless permits a fairly precise characterization of the 
major aspects of the homing process. Involved in this matter 
are: 1) the fact of almost simultaneous commencement of the 
return to the 'nest' on the part of the scattered members of one 
colony, 2) the fact that the duration of the feeding interval 
seems automatically fixed without reference to the rising of the 
tide, and 3) the evidence concerning central inhibition, already 
referred to in connection with the normal abeyance of heliotropic 
movements. To these points we shall return, after dealing ^^ ith 
the directed creeping toward the nest. 
The fact that Onchidia are able to return to their nest after 
being picked up and replaced at some other point within a cer- 
tain radius of the nest aperture is best appreciated from the 
perusal of such records as the following: 
July 1, 1914- Little Agar's Island. 
Five individuals were seen returning to a nest. Two of these were 
removed to the rock surface above the high-water mark (where, in 
our experience, these animals never wander naturally); the distance 
of the new point of departure was perhaps 40 cm. from the aperture 
of the nest. One of the displaced Onchidia turned directly toward 
the nest and crept straight back to it; the second one 'lost its way/ 
and wandered off in a strange direction. The three other members of 
the original group of five marched in a sort of triangular formation 
toward the nest aperture, two going to one side of the opening, the 
remaining one to the other side, then all three crept into the nest. 
