254 
Proceedings of the Royal Society of Edinburgh. [Sess. 
all other muscles to the second segment are cut, except when the leg is 
forcibly extended at the second joint. 
Fredericq draws his conclusions without taking this last fact into 
consideration. 
Demoor examined the process in Portunus and contradicted Fredericq. 
An external point d’appui, he says, is not necessary ; and autotomy at the 
breaking-plane probably takes place by the torsion of the '' partie caduqne’' 
of the leg on the basal part, the forces meeting at the breaking-plane, which 
is the locus of least resistance. He advances this view only as a theory, 
and at the same time points out that the reflex mechanism cannot be of 
such a simple nature as Fredericq would endeavour to show. It must, he 
says, be a highly complex reaction, involving to some degree most of the 
basal muscles of the leg. With this statement he finished his account of 
the subject, and since then no one has again taken it up. 
Fig. 20 (After Fredericq). — Explanation in text, 
c., carapace; h., body; l.e., long extensor. 
In the course of the present experiments, the movements of the long 
and short extensors were studied by means of graphical records of their 
contractions. 
Firstly, the combined tendons of the long and short extensors were 
attached to a heart lever and the cut end of the limb was stimulated by 
single induced shocks. 
The following were the results (see figs. 21, 22, 23, and 24). 
The traces show that there are two elements in the curve. The 
tendons of the long and short extensors were therefore isolated, and when 
this was done properly the following were the results. The flexor of the 
second segment was also attached to the lever, and it was found that 
it too contracted after a longer latent period than the two extensors. 
(Carcinus was used in this experiment.) (Fig. 25.) 
This demonstrated that the short extensor, contracted along with the 
“muscle disjoncteur” of Fredericq and with the flexor, probably played 
an important and independent part in autotomy. 
