1914-15.] The Reflexes of Autotomy in Decapods. 
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Section II. ANOMURA. 
Subsection I. Pagurids. 
Hermit Grabs. 
The Pagurids are lobster-like decapods characterised by shelter adapta- 
tion. The abdomen has become soft, and the posterior appendages have 
diminished in size, and act merely as a means of bracing the animal 
against the inner walls of its borrowed home. The most usual form of 
shelter taken by these animals is an empty whelk-shell, but one individual 
(Pylocheles) is found in Indian waters inhabiting the hollow inside of 
little pieces of water-logged bamboo. 
Whenever danger threatens a Pagurid it at once retires to the shelter of 
its shell by contraction of the thick abdominal muscles which grip the inner 
part of the spirals. This retiral is produced in very much the same manner 
as the back-swimming of the Palinura and Natan tia by tail-flapping. 
The type chosen for observation was Eupagurus bernhardus (Lin.), or 
the “ soldier hermit.” This animal is very plentifully got in trawling below 
tide marks, and it gets its martial name from its fierce method of attacking 
its neighbours and brothers. Hermit crabs, however, do very little real 
damage to one another. It is a rare occurrence to find one autotomised 
claw in a tank where upwards of fifty have been confined for several 
weeks. Loss of appendages in the natural habitat seems to be even more 
rare, and the number found regenerating is probably always under 
I per cent. It is interesting, therefore, to find that both autotomy and 
regeneration take place readily. 
It was found that if a chela or walking-leg be seized quickly and 
violently with forceps, the animal immediately withdraws to its shell and 
almost simultaneously the limb breaks off at a groove in the basi-ischium 
or second segment. The changes which take place in the basal muscles 
cannot be observed, for this part of the crab is hidden beneath the shell. 
After the leg has been autotomised it is found, on removing the animal 
from its shell, that the stump is firmly extended. If the tendon of the 
extensor be disconnected from its attachment at the base of the second 
segment, autotomy cannot occur. Whatever else happens at the time of 
injury, the extensor contracts violently, and remains contracted after the 
leg has been thrown off. 
In cases where the cut across a limb was quickly made and the stump 
freed, it was found, again, that the crab shot backwards into its shell. 
After a few minutes it emerged, and the damaged leg was seen to drop 
