TIIE CRAYFISH AND ITS ALLIES 119 



in the first larval stage. This power of defensive mutila- 

 tion occurs in those appendages which are most apt to be 

 seized, namely, the five thoracic legs, and is wholly 

 under the control of the reflex nervous system, for it may 

 occur when the entire voluntary nervous system has been 

 removed. The leg of a dead crustacean shows no such 

 capacity. If the leg of a lobster is cut off at some point 

 distal to that of normal rupture, the limb will later be 

 found cast off up to this point. Here a sort of double 

 membrane or diaphragm exists, with a central opening 

 only large enough to admit the passage of nerves and 

 blood-vessels. Upon rupture this passage is soon plugged 

 up by coagulated blood clearly a device to prevent ex- 

 cessive hemorrhages. Soon after a leg is cut off a papilla- 

 like body grows out from the stump of the limb, develops 

 into the shape of a small limb, and grows larger, with 

 each successive moult, until the normal size is reached. 

 The antennse, too, are much exposed to injury, but with 

 them autotomy is not practised. The}^ begin to grow out 

 at the place of injury, and at least one moult is necessary 

 for their complete restoration. 



Abnormalities in the claws of the lobster are not un- 

 common. The thumb-like protuberances of the next to 

 the last of the joints of the great claw is sometimes bifid, 

 or carries a large wart. The finger which opposes the 

 thumb is also sometimes forked (Fig. 116). Many of 

 these abnormalities are probably due to injury of the claw; 

 but others cannot be explained in this way. For instance, 

 cases have been observed of lobsters having crushing 

 claws of equal size on the two sides of the body. An 

 antenna has been seen replacing an eye, and this result 

 may be obtained by cutting off an eyestalk near its base 



