96 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



This table illustrates the fact that in the same lobster in which no 

 regeneration occurred below the breaking plane regeneration did take 

 place at this plane at a normal rate. It is evident from these re- 

 sults that while the thoracic appendages may and often do regener- 

 ate from other levels, the process is much slower in starting and there 

 is a large difference in the frequency of restoration avS compared with 

 regeneration at the breaking plane; in other words, the tendency to 

 regenerate a lost structure is much stronger and more highly de- 

 veloped at the normal breaking plane than at any other level in the 

 limb. 



In attempting to account for these facts the question is suggested 

 whether the difference in regenerative power at different levels may 

 not be best explained by the liability to injury and the action of 

 natural selection. As has already been intimated, it is a matter of 

 controversy whether the law of natural selection furnishes a satis- 

 factory explanation of the power of regeneration. A disputed 

 ciuestion in this controversy is whether there is any causal relation 

 between the liability to injury and the capacity for regeneration. 

 Weismann, for example, holds that there is such a causal relation, 

 while Morgan, on the contrary, maintains that no such relation 

 necessarily exists and that consequently natural selection is inade- 

 quate to explain the phenomenon of regeneration. 



Now it seems unquestionable that in the thoracic appendages the 

 breaking plane is the region of the limb most liable to final injury, 

 i. e., although the initial injury may be near the extremity, the -final 

 separation of the limb from the body usually occurs at the breaking 

 'plane. In all the lobsters taken from the traps during the summer 

 the lost limbs were nearly always separated at that place — a leg or 

 cheliped with half or two-thirds of the original number of segments 

 remaining is seldom found. Yet this condition might naturally be 

 expected. 



In experiments upor^ autotomy in the lobster it was foimd that if 

 the cheliped or leg was crushed by a pair of tweezers it was almost 

 invariably dropped at the breaking plane. This was especially 



