INSTINCT 105 



insect was swimming its efforts to swim away would be 

 performed with much greater vigor. If it does not effect 

 its escape by this method it has recourse to a remarkably 

 neat and apparently intelligent device. The hind legs are 

 thrown back as far as possible, whereby they are enabled 

 to grasp the breathing tube a short distance behind the 

 body; then by exerting a pull they bend the body ven- 

 trally. This soon places the second pair of legs so that the 

 offending object can be reached, when all four legs are em- 

 ployed to push the body away, which is very frequently 

 accomplished. The behavior of a decapitated Ranatra hi 

 this situation certainly affords an excellent simulation, not 

 only of purposive action, but also of considerable ingenuity 

 in its accomplishment. 



The reactions of the brainless frog form the stock illus- 

 trations of reflex action. The withdrawal of a foot when 

 pinched is one of the simplest of these. When a drop of 

 acid is placed on one side of the body the hind foot of that 

 side is brought forward to wipe it off. With a somewhat 

 stronger stimulus the fore leg of the same side may be 

 moved back to the irritated spot. If the acid is placed on 

 the middle of the posterior part of the back both hind legs 

 are employed to remove it. We have here reflexes of a 

 higher degree of complexity involving the coordinated move- 

 ments of many muscles. If a frog with the greater part of 

 its brain removed is taken in the hands it uses both hind 

 legs to push against the hands, and at the same time inflates 

 the lungs with air, causing the body to swell so that it more 

 readily slips from the grasp. The use of the hind limbs 

 and the swelling of the body may be regarded as two com- 

 plex refle es excited by the same cause and which cooperate 

 to enable the animal to effect its escape, but the behavior 

 may equally well be described as an instinctive reaction. 



