242 Proceedings of the Royal Society of Edinburgh. [Sess. 
When the cut end of the limb is continuously stimulated by rapidly 
interrupted induced shocks (Neef s hammer), contractions of the extensor 
muscle last several seconds and are repeated after a definite period. This 
also happens when the nerve segment is isolated. 
In some cases a peculiar rhythmic contraction of the extensor of the 
second segment may be recorded when electrical stimulation is used 
(figs. 13 and 14). 
Owing to the inaccessibility of the tendon of the flexor of the third 
segment, the time of its contraction and its latent period cannot be recorded. 
Fig. 13. — Rhythmic contractions of the extensor of the second segment. 
(The speed of drum same as in fig. 12.) 
Fig. 14. — The same with slower drum. 
but I believe that it contracts after the extensor of the second segment 
and before tail-flapping begins. 
Study of muscle-contraction in the case of chelipeds is also prevented 
by the overhanging carapace, but, as the mechanism is very much the same 
as that found in the higher Brachyura, detailed examination is unnecessary. 
This point, however, may be mentioned: the break which takes place 
after autotomy occurs at a definite groove in the basi-ischium or second 
limb-segment. This segment is probably the product of fusion of two 
parts, represented in the walking-legs by the second and third segments. 
The break is clean as a knife-cut, and involves calcareous material at all 
points. This stands in marked contrast to what is seen in the case of the 
walking-legs, where the ring of cut surface is partly calcareous and 
partly membraneous. Of great importance, too, is the fact that after 
