ii8 THE BIOLOGY OF THE SEA-SHORE 



criticism need not, however, greatly disturb us in this case, 

 since it is directed chiefly against the Darwinian theory of 

 the manner in which adaptations arise, and he does not, 

 as in the case of regeneration, deny the influence of the 

 environment. Certainly, in some cases, a relation between 

 autotomy and the problems of the environment does appear 

 to exist, and Morgan himself can find no other explanation 

 of autotomy than " as an adaptive response of the organism 

 to its conditions of life." We may now, however, leave 

 general considerations on one side and turn to an examination 

 of the numerous cases of autotomy encountered on the 

 shore. 



Autotomy and Regeneration in Decapod Crustacea. — 

 The faculty of shedding a limb is found in a number of 

 crustaceans, but varies considerably in the degree of its 

 elaboration. Basing our account on recent work by Paul 

 (1915), we may begin, as he does, by considering the prawn 

 {Leander squilla), which exhibits autotomy in its least 

 specialised form. 



When seized roughly by a leg the prawn extends the 

 basal segment and, jerking itself backwards by a violent 

 flap of its tail, causes the leg to fall off^ at the joint between 

 the second and third segments. This is the normal form of 

 autotomy, and in prawns taken from the sea with a leg missing 

 the break has always taken place at this precise point. 

 A curious modification of behaviour is seen, however, when 

 a limb is severed quickly with sharp scissors. The backward 

 jump still takes place, but the limb is not autotomised and 

 the animal, on quieting down, flexes it in towards the 

 mouth and begins pulling at it with its jaws (autophagy). 

 Later, the limb resumes its normal position except that for 

 a brief period the next sound joint is sharply flexed, a process 

 which is thought to limit haemorrhage. 



In the lobster the process of autotomy is developed a 

 step further. The rupture of the walking leg takes place, 

 as in the prawn, at the region of the joint between the 

 second and third segments, but a new element has now made 

 its appearance, since the break, instead of involving only a 



