314 THE ZOOLOGIST. 
are animals actuated by the varied motives which influence 
reasoning mankind, subdued and modified, as a matter of 
necessity, from imperfection in their structural detail ? 
Carlyle has quaintly said that ‘“ the two great moving powers 
of society are hunger and the policeman.” Sternly inexorable is 
the former, a humiliating necessity the latter. Now as animals 
must eat to live, it is not unnatural that they should be found 
abroad at such times as their prey is most easily procurable. 
Moreover, they have cautiously to avoid their own enemies, and 
thus find safety in feeding under cover of darkness. But besides 
the craving for food there seems another influence which, though 
at first less recognizable, is possibly much stronger in its potency 
—namely, an inclination to seek shade. Throughout the animal 
kingdom generally, but. more especially among the lower forms, 
examples of this are numerous. Coincident with an uncomfortable 
feeling, howsvever produced, is retirement to shade. In short, 
light acts as a stimulus, not equally shared by all creatures. 
Its influence on protoplasmic matter is evident, and is of con- 
tinual occurrence even among animals of most imperfect organi- 
zation. ‘Traced upwards from these, the reception of sensory 
stimuli presents us with superadded or adaptive structural modi- 
fications often rendered acute to a degree. 
How gradual development from simple to more differentiated 
condifions has been brought about in the march of time, and 
what may be the relation of transmission of qualities from parent 
to offspring I leave unanswered as involving discussion apart 
from the immediate purport of this article. 
Premising that nocturnal activity is the sequence of an 
endeavour to shun light, as annoying or detrimental to the 
organism, and that in certain cases search for food or other 
functional impulse necessitates nocturnal habits, I shall confine 
my remarks accordingly. 
In using the term ‘nocturnal,’ I would wish it to be 
understood in its widest sense. Thus the great mass of animals 
are abroad, feed, and otherwise are actively employed, so to say, 
in their business of life, during daylight and sunshine, that is, 
from morn till eve. Not a few, however, from preference or 
necessity, are then in retirement, from which they only emerge 
between nightfall and sunrise. Others choose twilight or the 
“gloaming”—that hazy obscurity which precedes the setting in 
- . . oes 
