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Proceedings of the Eoyal Society of Edinburgh. [Sess. 
attempts at removal by the maxillipeds and other legs followed the 
retreat of the animal. The same has been described in the lobster, and it 
is pointed out, in addition, that the chelate walking-legs can often be seen 
to remove a damaged limb at the proper breaking level. 
The Crayfish. 
In structure the fresh-water crayfish (Astacus fiuviatilis (Fabr.)) closely 
resembles the lobster. The animal could not be studied in its natural 
habitat, and the conclusions drawn are from laboratory observations only. 
The crayfish behaves in almost a similar manner to the lobster when 
its limbs are mutilated. Autotomy of all legs at the base may occur. 
There is this difference, however : the chelipeds are abandoned on a very 
much weaker stimulation, in comparison to size, than in the lobster. On 
the other hand, walking-legs are autotomised much less readily. 
In a paper on regeneration of the first leg in crayfish, Reed (7) points 
out the necessity of holding a mutilated walking-leg in order that the 
animal may autotomise, but she mentions nothing about the tail-flappings 
At the same time she states that rupture occurs at the “ free joint between 
the second and third segments of the limb,” implying that only a tearing 
of synovial membrane occurs. I examined the stump of a walking-leg 
after self-amputation, and found the same half-ring of calcified material 
carried away from the third segment as in the lobster. As the flexor 
muscle remains firmly contracted, the ring is drawn into the cavity of the 
second segment, and may be so sunken in the soft tissues that it cannot 
be seen. 
Although no tracings have been taken, there is little doubt but that^ 
as in the lobster, a definite time-relation exists between the various muscle 
contractions. First, the limb is extended at the second joint; then the 
flexor of the third segment, which weakens this segment in the region of 
its base, contracts. These movements are quickly succeeded by rapid 
tail-flapping and autotomy at the weakest point, i.e. the groove in the 
third segment. 
If no resistance be offered to the walking-leg, and if the scissors be 
quickly disengaged, tearing movements of the other legs and jaws occur 
markedly. The chelipeds, also, can very effectively pull off a damaged 
walking-leg if they are able to get hold of it. This form of removal has 
reached a high degree of development in the hermit crab, and it will bo 
discussed fully at a later point. 
