170 LECTUEES ON BIOLOGY 



hitherto been greatly exaggerated. But this conviction does 

 not detract from the fact that the organic world is infinitely 

 rich in adaptive arrangements. Almost inexhaustible seem the 

 means with which Nature furnishes her children, in order to 

 make them better fitted for the struggle for existence ; but since 

 to mention such organs of adaptation by name only would require 

 volumes, we must be content with a few of the most characteristic 

 instances. 



We read frequently in the newspapers reports of a conscript 

 having cut off a finger or a toe in order to escape military 

 service. Few people know that similar cases of self-mutilation or 

 autotomy are common in the animal kingdom. It is not easy 

 to give a strict definition of this remarkable process, because 

 autotomy represents in one direction a transition into another 

 biological process asexual reproduction by fission, or budding; 

 on the other hand, it is questionable whether, for instance, the 

 disintegration of many protozoa, in consequence of certain 

 stimuli, may be regarded as self-mutilation, because in this 

 process the whole animal is destroyed. The best definition is 

 probably that autotomy is a physiological process due to the 

 effects of stimuli of varying kinds, whereby one part of the body 

 is sacrificed in order to save the whole. It is an adaptation of 

 the organism to definite demands of the conditions of life. 



I well remember the painful disappointment which I felt 

 as a boy when, after a tiring hunt for lizards, I had at last been 

 successful in catching one by the tail, only to be left in possession 

 of the tail, whilst the lizard itself had long disappeared in the 

 grass. It is remarkable with what rapidity the dismemberment 

 of the tail takes place : a few vigorous striking and twisting move- 

 ments of the lizard, and the operation is over. The amputation 

 does not take place, as one would be inclined to assume, between 

 two vertebrae, but right in the middle of one of the caudal 

 vertebrae. From the seventh caudal vertebra, counting from the 

 base, the vertebrae are enlarged to double their normal size and 

 formed in the shape of an hour-glass. At the thinnest point there 

 is a small non-osseous partition-wall, and it is here where the 

 fracture takes place. 



A simple experiment will show that the separation of the 

 tail takes place quite independently of the animal's volition, 



