235 
1914-15.] The Eeflexes of Autotomy in Decapods. 
no heavy chelate claws like those possessed by the latter. The prawn has 
therefore very little provision for defence. The limbs have six segments, 
and the first and second pairs of each side are pincered. 
In prawns collected from the contents of a trawl, very few are found 
which have lost a leg. In those which I have seen short of limbs, the 
break has always taken place at the free joint between the second and 
third segments. The following observations were made on the results 
of mutilation : — 
(a) When any part of the limb distal to the second segment is sharply 
cut across by scissors, the prawn (under water) immediately shoots back- 
wards on account of a violent swimming movement or flap of its powerful 
tail. When it comes to rest it is found that the stump is rigidly extended 
Fig. 1. — The leg of the prawn, showing how the sound 
joint next to the cut end is sharply flexed, and 
haemorrhage prevented. 
owing to violent contraction of the extensor muscle of the second limb- 
segment. This condition lasts for about thirty seconds, and the limb is 
then flexed inwards to the jaws. Here it is subjected to violent pulling 
for several minutes, but soon the animal quietens. The limb then takes 
up its normal walking position, with this exception, however, that the 
next sound joint is sharply flexed (fig. I). This sequence of events follows 
every instance of quick and clean cutting across one of the distal segments, 
with almost always the same time [relations. Prawns treated in this 
manner never cast off the stump of the limb, even after many weeks, and, 
as a rule, the sharp flexion at the next sound joint to the cut surface has 
disappeared in twenty-four hours. 
(6) When clumsy scissors are employed in mutilating, which cannot be 
disengaged from the leg before the violent tail movement takes place, the 
leg, from the third segment distally, is thrown off' as the animal escapes. 
The break is found to be identical with that seen in prawns taken from 
the sea with a leg missing (fig. 2). 
