THEORIES OF AUTO TOMY 1 5 5 



able if this spider had acquired the habit in connection with the better 

 regeneration of the leg at the base, since the leg can presumably also 

 regenerate at any level, as in the epeirids. 



In this same connection I may record that in the hermit-crab I 

 have often observed that when a leg is cut off outside of the break- 

 ing-joint, if the leg is not thrown off at once, the claws of the first 

 legs catch hold of the stump and, pulling at the leg, offer sufficient 

 resistance for the leg to break off at the breaking-joint. I cannot 

 believe that this instinct has anything to do with the better regenera- 

 tion of the leg at the coxal joint, however attractive such an hypothesis 

 may appear. 



THEORIES OF AUTOTOMY 



A number of writers have pointed out that under certain condi- 

 tions it is an obvious advantage to the animal to be able to throw off 

 a portion of the body and thereby escape from an enemy. It has 

 been suggested that if a crab is seized by the leg, the animal may 

 save its life at times at the expense of its leg ; and since the crab has 

 the power of regenerating a new leg, it is the gainer in the long run 

 by the sacrifice. The holothurian, that ejects its viscera, has been 

 supposed to offer a sufficient reward to its hungry enemy, and escapes 

 paying the death penalty, at the expense of its digestive tract. Thus, 

 having shown that the process of autotomy is a useful one, it is 

 claimed that it must have been acquired through a process of natural 

 selection ! An equally common opinion is that autotomy is an adap- 

 tation for regeneration, since in certain cases, as in that of the crab's 

 leg, better conditions for subsequent regeneration occur at the break- 

 ing-joint than when the amputation takes place at any other region. 

 Since less bleeding takes place when the crab's leg is thrown off at 

 the breaking-joint, and since the wound closes more quickly when 

 the arm of the starfish is lost at the base, it is assumed that we have 

 in both cases an adaptation to meet accidents, and that the adaptation 

 has been acquired by natural selection. 



A consideration of these questions involves us once more in a dis- 

 cussion of the theory of natural selection. An attempt has been made 

 in another place (pages 108-1 10) to show that we are not justified in 

 assuming that because a process is useful, therefore it must have been 

 acquired by means of natural selection. Even if it were granted that 

 the theory of natural selection is correct, it does not follow that all 

 useful processes have arisen under its guidance. We may, therefore, 

 leave the general question aside, and inquire whether the process of 

 autotomy could have arisen through natural selection (admitting that 

 there is such a process, for the sake of the present argument), or 

 whether autotomy must be due to something else. 



