130 THE BIOLOGY OF THE SEA-SHORE 



tion on the sea-shore has disclosed anumber of interesting facts 

 it has not enabled us to reach any one explanation which will 

 apply to every case of these phenomena. There is a general 

 tendency to regard autotomy as of value as a means of escape 

 from enemies, or, at any rate, as an adaptive response to 

 particular features of the environment. Among the facts 

 which lend colour to this view are the restricted occurrence 

 of autotomy in general and its relatively frequent occurrence 

 on the sea-shore, where the struggle for existence is admitted 

 to be particularly severe. Thus, the remarkable structure 

 at the breaking plane in the crab's leg, whereby bleeding is 

 reduced to a minimum, is regarded by Paul as having arisen 

 in connection with the tendency of shore crabs to have their 

 limbs crushed by stones. The reality of the danger is 

 thought to be proved by the number of crabs which are found 

 to have lost a leg in natural conditions, the proportion on 

 rocky shores after winter storms being as high as fifty per 

 cent. The autotomy of the legs and chelas of the lobster, 

 on the other hand, is interpreted as providing a means of 

 escape from enemies, but the evidence for this view is of a 

 more slender nature than that adduced in the case of the 

 common shore crab. So far as the autotomy of starfishes 

 and the self-evisceration of Holothurians are concerned 

 the adaptive nature of these processes is, apart from 

 one or two observations, almost entirely a matter of 

 conjecture. 



Some cases of what we call " autotomy " may be nothing 

 more than the normal asexual methods of reproduction, and 

 others may be responses of a pathological nature to unaccus- 

 tomed stimuli. Our own conclusion is that it is perhaps not 

 impossible that the tendency of lower multicellular animals 

 to reproduce by fission may have formed the raw material 

 upon which, under the stimulus of the shore struggle, 

 natural selection may have worked in order to produce the 

 more specialised forms of autotomy as seen, let us say, in 

 the shore crab. The tendency towards fission, in turn, may 

 be referred back to considerations of a mechanical kind such 

 as weak lines occasioned by axial growth increase {cf. D'Arcy 



