236 Proceedings of the Koyal Society of Edinburgh. [Sess. 
(c) To follow further the indications of the nature of what we must 
regard as normal autotomy in the prawn (namely, division of the leg 
between the second and third limb-segments), an individual may be fixed 
in a hardening fluid with some of the legs fully extended at the|second 
Fig. 2. — The leg of the prawn, showing the position of the first three limb-segments when division is taking place. 
articulation, and others fully flexed. It is then found that the application 
of almost equal pulling forces at the ends of the limbs causes rupture at 
the junction of body and first segment in the first case, but rupture between 
the second and third segments in the second case (fig. 3). In the former 
Fig. 3. — The prawm. 1 is the plane of division when the 
leg is fully flexed ; 2, when it is fully extended. The 
arrow indicates the direction of traction. 
the leg pulls with it all the muscles which find attachment to the body 
skeleton, and leaves a large wound ; in the latter the break is almost clean, 
and the rupture-surface comparatively small. 
The following conclusions on the nature of autotomy in this decapod 
may therefore be drawn from the above experiments : — 
(I) Since autotomy does not follow quick and clean cutting across a 
limb, evasion is its chief purpose. 
