172 SECRETS OF ANIMAL LIFE 
across the interior of the hollow limb at the breaking- 
plane, leaving a foramen for nerve and artery. This 
diaphragm consists of two flaps, and when autotomy 
occurs “ these are forced together by relative change 
of pressure on the outer side.” They act as a valve, 
“and the moment autotomy takes place bleeding 
is stopped.” We feel ourselves in the theater of 
a great surgeon whose knife staunches as it cuts. 
We are reminded also of the partition which in 
autumn grows across the insertion of the leaf-stalk 
and closes the wound as it separates off the wither- 
ing leaf. 
We see, then, that the surrender of a limb is of 
common occurrence in higher Crustaceans. It often 
secures escape; it also avoids bleeding to death 
if a limb has been badly wounded by an enemy or 
bruised by the movement of stones on a storm- 
swept shore. We find, moreover, that it sometimes 
occurs rather roughly and sometimes with great 
neatness; that it sometimes involves several acts 
in a chain and sometimes only one. And the very 
interesting general result reached by Mr. Herbert 
Paul’s fine experiments is that in those higher 
Crustaceans, such as crabs, where the breaking 
joint is structurally most complex, the physio- 
logical reflex process is simplest. It is a single 
reflex, whereas in lower forms there may be several 
links in the chain of events. In the crab, as he says, 
there has come about in the course of time a short- 
circuiting of a “current” which in lower forms 
has a much leneer path. Such occasional returns 
