196 SECRETS OF ANIMAL LIFE 
hibited by types which have, so far as we can judge, 
very little of the roving spirit in their composition. 
Weare far from saying that there are not tempera- 
mental rovers among animals. The common crab 
has been known to journey along the sea-floor 
for about a hundred miles, and a cod may take a 
jaunt of several hundreds, but our point is that 
wanderings like those of locusts and lemmings, 
badly called migrations, are reactions to lack of 
food. We have admitted the probability that there 
might not be these effective racial reactions to-day, 
had there not arisen long ago variants with a rest- 
less, experimental, exploring, roving disposition, 
who conquered difficulties by circumventing and 
evading them, who went on a journey, discovering 
the truth of solvitur ambulando; but what we main- 
tain is that locusts and lemmings are not “ rovers ” 
now. In the same way we cannot accept the 
American biologist’s suggestion that “ nomadism 
in man is of the same order as that of birds,” for 
bird-migration is a long-established, smoothly- 
working, regularized alternation between the feed- 
ing and resting of the winter quarters and the 
breeding and nesting of the summer quarters. It 
probably began in individual variations or muta- 
tions in the direction of “roving,” but the instinct 
has been established and perfected in definite rela- 
tion to the actual necessities of nutrition and repro- 
duction as affected by seasonal changes. 
It is important not to think of the human “ rover ” 
as necessarily pathological, for whether he is one in 
