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 clielipeds 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, tw T o 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 Reaumur (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, Garcinus mamas. 
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 with it. The fracture of the leg of a living crab occurs, as we 
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