14 CONTROLLED NATURAL SELECTION 
enemy by making some menacing movement ; 
even quite small animals, insects for instance, 
will then make threatening motions. Under 
Repellent motions would also be classed Warn- 
ing motions; those which presuppose know- 
ledge on the part of the enemy, the attacker ; 
a knowledge gained by previous association of 
the motion with some unpleasantness. There 
is considerable evidence that this kind of 
motion is frequently mimicked. 
These signals by movement are, as a rule, 
associated with numerous other displays— 
displays of position, attitude, colour, sound, 
and scent; for this reason they are difficult 
to analyse. It is often difficult to decide 
whether the motion is the essential or an 
accessory of the signal. 
(2) Attractive-—Motion signals, whose pur- 
pose is to attract an enemy, although fre- 
quently overlooked, are also common in 
Nature. Amongst birds, as mentioned in 
Chapters V and X under Family Instincts, 
parents will frequently endeavour, by the 
making of conspicuous movements, to attract 
an enemy, to draw its attack. Numerous 
other examples will be given when considera- 
tion is made of Sexual Displays. Purposely 
conspicuous movement is probably, therefore, 
