No. 493] 



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5 



Regeneration after Removing a Bone some Distance 

 from the Cut End 

 In order to see what would happen if the bones are 

 absent at the cut surface, the hind leg of Dienryctylus 

 was cut off above the knee, the greater part of the femur 

 was removed from the stump, and the skin sewed over 

 the cut end. Regeneration of a new leg was delayed, 

 but took place. The stump of the leg seemed to contract 

 somewhat, so that the cut end of the bone was brought 

 nearer to the cut end of the muscles. The prolifera- 

 tion from the end of the bone must have grown down 

 to the cut surface, and then, extending beyond this, given 

 rise to the material for the skeleton of the new leg. The 

 experiment shows the possibility of the same thing occur- 

 ring when a grafted piece is pushed aside. Unless the 

 graft block the proliferation from the bones of the stump, 

 these may contribute material to the new limb. 



adult frogs numerous experiments have been made dur- 

 ing three winters. Pieces of the leg were cut off, and 

 grafted in skin-pockets in various ways, but without 

 results. I hoped that the breaking down of such grafted 

 pieces might incite the regeneration process, if its ab- 

 sence in frogs were due simply to some retarding influence 

 in the method of closure of the cut surface as occasionally 

 occurs in pieces of other animals that have well developed 

 powers of regeneration. 



Pieces of the leg of tadpoles (without the skin) were 

 also inserted into the leg of the frog without inciting 

 regeneration, but as different species were probably used 

 for graft and stock, successful results were less to be 

 expected. Pieces of the muscles and other tissues of the 

 tadpole's tail were inserted in skin-pockets of the leg of 

 the frog but without effect. Since the tail of the tad- 

 pole has remarkable powers of regeneration, it seemed 



