Chapter IV.— DEFENSIVE MUTILATION AND REGENERATION OF LOST PARTS. 



AUTOTOMY IN THE YOUNG AND ADULT. 



It is well known that among the invertebrates the Crustacea possess, in a 

 remarkable degree, the power of reproducing parts of their bodies which have been 

 lost. This is most pronounced in those Decapods, such as the crab and lobster, which 

 practice defensive mutilation or autotomy. Thus, if one catches aland crab and holds 

 it by the carapace it brandishes its chelipeds in its vain attempts to get free, but once 

 seize it by the claws, the crab immediately scuttles off, leaving you in possession of 

 its only effectual weapons. The leg is broken off at a definite place near its base; 

 there is very little bleeding from the old stump, and a new limb soon sprouts and 

 grows again. This power of thus detaching a limb at the right time is a valuable 

 means of defense, which, as Pere Du Tertre remarked, would be very useful for pick- 

 pockets. The lobster has the power of casting off its legs, but those which carry the 

 "nippers" are the most commonly sacrificed. 



The limb (cut 6, plate B) consists of seven joints, two basal ones — coxopodite (1) 

 and basipodite (2) — and five succeeding joints, the last two of which form the claw 

 (6 and 7, cut 6). In autotomy the five terminal joints are always cast off; that is, frac- 

 ture takes place between the second and third segments. In the large chelipeds of the 

 lobster the second and third joints — basipodite (2) and ischiopodite (3) — are fused 

 together. This is the case in all the pereiopods of the crab. There is a distinct groove 

 which marks the union of the two fused joints, and it is always in this groove that 

 disjunction occurs (x, cut 13, plate D). This fact was noticed by Eeaumur {161) at the 

 beginning of the last century, but he did not offer an explanation. He noticed that it 

 was not at the functional articulation that the limb was broken, and that the shell of 

 the "second joint" (second and third, cut 13) was "composed of several different 

 pieces. The evidence of this was found in the presence of two and sometimes three 

 sutures, which occur in this .part. It is in the middle suture, moreover, that the leg 

 is broken." He noticed also that the leg could be broken off by exerting very little 

 force. The interesting fact did not escape his attention that if you cut off the leg at 

 or near the terminal joint you will find after a time that the mutilated limb is always 

 thrown off at the suture between the second and third joints. 



Fredericq (71) has published several papers on the defensive mutilation of the 

 crab, and has given a physiological explanation of this phenomenon. I will now add 

 a brief abstract of some of his experiments, which were performed chiefly upon the 

 common green crab, Carcimis mcenas. 



The breaking off of a leg, which so often happens when we handle these animals, 

 is not due to their fragility, for experiment proves that the limbs of a dead crab are very 

 resistant and that they will support a weight of 3£ to 5 kilograms (7.7 to 11 pounds), 

 which represents about one hundred times the weight of the entire body of the animal. 

 If one breaks off a leg of a dead crab, it separates either between the cephalothorax 

 and first joint, or between the first and second joints, and a mass of muscles is usually 

 drawn out of the body Avith it. The fracture of the leg of a living crab occurs, as Ave 

 100 



