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.' 1 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 lon^r path. Such occasional returns 



