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SOME NEW POINTS ON AUTOTOMY AMONG 

 THE DECAPOD CRUSTACEA. 



By J. HERBERT PAUL, M.A., B.Sc, 

 Barbour Research Schoiar in Physiology at the University of Glasqow. 



The self-amputation of injured parts by different animals 

 has been described and recorded since the fifteenth century, but 

 it was only at the end of the eighties of last century that exact 

 observations were made. Fredericq * then analysed the process 

 of autotomy in Garcinus moenas, paying special attention to the 

 neuro -muscular mechanism and the structure of the breaking- 

 joint at the limb-base, but since his time very little real knowledge 

 has been added to the subject. 



In the shore-crab, autotomy is seen in its most highly developed 

 form. It is a unisegmental reflex, for it occurs when the nerve 

 cord above and below the segment of injury is cut. If a leg be 

 cut, crushed, burned, or otherwise severely damaged at any point 

 central to the terminal segment, it is immediately extended against 

 the carapace, and usually snaps off at a groove in the second seg- 

 ment or basi-ischium called the breaking-plane. If the crab be 

 suspended by one of its legs, and the necessary stimulus for 

 autotomy applied, it at once drops to the ground, leaving the part 

 of damaged Umb distal to the breaking-plane in the hand of the 

 operator. 



It would be natural to conclude that the region of the breaking- 

 plane is the weakest part of the leg, but Fredericq demonstrated 

 that this is not the case. He suspended a crab by one of its legs, 

 and attached weights to the body till the leg was torn off. The 

 break occurred at the joint between the body and the first segment, 

 and not at the breaking-plane. The rupture surface was large 

 and irregular, and division took place only when many times the 

 body weight had been added. 



Fredericq attributed the process of self -amputation to vigorous 

 contraction of the long extensor muscle of the second limb segment, 



