306 CHARLES ALBERT SHULL. 



However if the injury actually took place as indicated in the 

 diagram referred to above, the most plausible explanation which 

 can be offered is in harmony with Bateson's statement. The 

 regeneration should lead theoretically to triplication, that is, to 

 the production of three appendages, two supernumerary ones on 

 each cut appendage ; and these on the right side of the body 

 should stand as a left between two rights. The abnormal 

 pleiopod shows defective regeneration only in the suppression of 

 the exopodite of the anterior supernumerary appendage. The 

 rounded projection of the first accessory pleiopod may be ex- 

 plained similarly as the fused basal portions of the two super- 

 numeraries, whose tapering jointed ends have been completely 

 suppressed. 



The abnormalities have probably arisen after an injury caused 

 by some force acting in the direction of the arrow in the diagram, 

 Fig. 17, which produced two breaking surfaces, from which the 

 new pleiopods arose, following the laws of symmetry for super- 

 numerary appendages as stated by Bateson. 



The abnormal appendage shown in Fig. 3, is a case of back- 

 ward homoeosis. It would be of interest to know the hereditary 

 behavior of such unisexual characters if bred in confinement. 



B. Experiments. - - Few investigations of the regenerative power 

 of the abdominal appendages of the Decapoda have been made, 

 and the results obtained have not been entirely satisfactory. 

 Morgan's experiments on Eupagunts longicarpus in 1898 showed 

 that a slight power of regeneration existed in the appendages of 

 two or three of the individuals he used ; but his experiments ex- 

 tended over too brief a period of time to secure any marked 

 regeneration. The first experiment was continued only twenty 

 days, and the second for twenty-eight days. And the conditions 

 under which the material was kept were possibly not the most 

 sanitary, as the fact that over 40 per cent, of the individuals died 

 during the twenty-eight days would seem to indicate. One 

 would hardly expect regeneration to be rapid under conditions in 

 which life itself could scarcely be maintained. My experience 

 has shown that although regeneration may occur after an opera- 

 tion, and become visible without an intervening moult, it usually 

 does not do so in the pleiopods. None of the individuals Morgan 

 used was kept until a moult had occurred. 



