7 8 Instinct and Intelligence 



crayfish than in earthworms, the ordinary in- 

 stinctive movements of the former animals are 

 of a distinctly higher order than those displayed 

 by the latter. For instance, a crayfish with its 

 head, claws, and long feelers protruding from 

 its burrow keeps a careful watch on the divers 

 objects floating near it in the surrounding 

 water, and whatever these may be, they are 

 seized by the animal's claws, torn to shreds by 

 its capacious jaws, and passed into the 

 creature's mouth. It is said these animals even 

 devour their own spouses. Crayfish exercise 

 no discrimination in the choice of their food ; 

 anything floating within its reach acts as a 

 stimulus on the animal's visual nervous system, 

 a stimulus which becomes manifest in the pur- 

 posive movements of certain groups of muscles, 

 leading to the effective grasping of the object 

 which set the neuro-muscular machinery in 

 action. The adjustment of such movements to 

 the incidence of external stimuli is doubtless 

 facilitated by the excitation of the animal's 

 tactile sensory organs or setae which abound on 

 his antennae. These feelers are constantly 

 waving about in the surrounding water, and are 



