HOMING OF SEA-SWALLOWS 4 
It is a familiar step in scientific method to try to 
bring an obscure fact into line with others of an 
approximately similar kind, and this must be done 
in the case of the homing terns, In this connection 
it is unfortunate that the data in regard to homing 
dogs and cats and other mammals are not in a form 
suitable for scientific purposes, and that crucial 
experiments to show what untrained homing pigeons 
can do are lacking. 
Exceedingly careful experimental work has been 
done with ants and bees, which find their way 
home successfully within a limited radius, and the 
balance of evidence inclines to the conclusion that 
most of the phenomena can be explained by the 
gradual registration of various sets of stimuli— 
olfactory, tactile, visual, and kinesthetic. Here 
also, however, there are residual phenomena at 
present as inexplicable as the homing of the terns 
from Galveston to the Tortugas. Professor Watson 
holds the chair of Experimental and. Comparative 
Psychology at the Johns Hopkins University, and 
his experimental study of the homing terns is 
marked by a greater psychological subtlety than is 
usually to be found in the adventures of zoologists 
in similar fields. Thus it is interesting to notice his 
careful observations on the duration of the nesting 
impulse when the normal activities have been inter- 
rupted. He finds that it remains strong for two or 
three weeks; and this should be borne in mind, for it 
gives an illuminating significance to the homing of 
the sea-swallows, They are returning to their nests, 
