AUTOTOMY AND REGENERATION 121 



diaphragm are forced over it owing to the great increase in 

 pressure on the outer side of the membrane. Meeting 

 together, the flaps at once stop bleeding " (Paul, op. at.). 



The question will possibly occur to the reader as to 

 whether the blood of these Crustacea possesses special clotting 

 powers which would aid in the prevention of hemorrhage 

 after autotomy. Tait (1913), however, who has made ex- 

 periments in this direction, has not been able to establish 

 a relation between the degree of blood coagulation and the 

 process of autotomy. 



Other remarkable facts have been elucidated by Paul as 

 to the manner in which a new limb is regenerated. Regenera- 

 tion of the limb begins immediately after autotomy by the 

 growth of epidermal cells over the stump, and eventually a 

 papilla is formed which is really a limb in miniature. The 

 new limb remains in this condition until immediately 

 following a moult, when it is apparently at once expanded to 

 several times its previous size. This laying down of the 

 limb in miniature and its expansion only when it is almost 

 ready for use is in remarkable contrast to the gradual process 

 of regeneration seen in other groups, and, according to Paul, 

 must be interpreted as a beautiful adaptation to the needs 

 of the animal, since the latter would only be hampered by the 

 presence of a gradually regenerating limb. Similarly, the 

 form of the papilla would also be adaptive. In the lobster 

 which, in natural circumstances, spends all its time under 

 water, the miniature limb is straight, is covered by only 

 a thin layer of uncalcified chitin, and requires the presence 

 of water for its support. In the shore crab, however, which 

 spends a large part of its time out of water, the papilla is 

 compactly rolled (it may be folded on itself three times) 

 within a tough envelope, and is quite firm in the air as well 

 as in water. The hermit crab is said to be intermediate 

 between these two other forms both as to its habits and as 

 to the shape of its papilla. 



It is evident from the foregoing account that Paul is in 

 no doubt as to the adaptive nature, in Decapods, both of 

 the process of autotomy and of that of regeneration. He gives 



