THE FACTORS OF EVOLUTION 171 



being purely a reflex-action. This independence is so complete 

 that lizards which have been beheaded or cut up, throw off 

 the tail on receiving a stimulus at the tail-end, exactly like 

 healthy animals. Investigations further proved that the reflex 

 centre lies in the spine between the posterior extremities in the 

 so-called lumbar region, for if we cut a lizard in two below the 

 tail-extremities self-amputation does not take place. 



Mutilation is chiefly performed by the tail-muscles, and it 

 requires a vigorous effort on the part of the animal to rid itself 

 of its tail. Thus it is that only healthy and strong lizards are 

 capable of self-mutilation, while those that are exhausted by 

 hunger or frost have not the power to do so. It is interesting to 

 note that after death it is as difficult to break off the tail as it 

 is to break off one of the legs, and it is further remarkable that 

 in that case the tail usually breaks in any other but the normal 

 place. 



Immediately upon self-mutilation the muscles of the stump 

 contract to prevent haemorrhage. After a few days the wound 

 is healed, a new tail-end begins to grow, and in a few months 

 the damage has been repaired. Sometimes during the healing 

 process peculiar malformations occur, and in the place of one 

 tail two or three are formed. Aldrovandus even recorded a case 

 of a four-tailed lizard. Though a mutilated lizard is no doubt 

 at first harassed in its movements, the advantage which it derives 

 from this faculty of autotomy is obvious, since it is probably in 

 most cases the tail by which the lizard-hunter succeeds in grasp- 

 ing the agile animal. 



In crustaceans and other arthropods self-mutilation is equally 

 general, but here it is chiefly legs and claws which are freely 

 sacrificed. The females of termites and ants at the end of their 

 nuptial flight break off their wings which in their future domestic 

 life would only be a hindrance to them. It has frequently been 

 observed how these intelligent animals help one another in 

 performing this operation. 



The most peculiar behaviour is shown by many species of 

 locusts, of which it is exceedingly difficult to obtain uninjured 

 specimens. No sooner are they caught than they push the 

 captured leg or wing between their powerful jaws and bite it 

 off. Though ineffective with man, this self-mutilation probably 



