I/O 



T. H. MORGAN. 



the large claw by the simple operation of removing the large 

 claw of the other side. At the next moult the small claw be- 

 comes the big one, and the newly regenerated claw becomes 

 the small one. Zeleny 1 found in 1902 that a similar throwing 

 over of the large operculum of the annelid, Hydroidcs, can be 

 brought about by the same sort of operation. Wilson - in 1903 

 made some important additions to Przibram's work, using an 

 American species of Alpheus. He suggested that the small claw 

 is merely an arrested stage of development of the big claw, and 

 that when the big claw is removed the check is at the same time 

 taken away that holds back the development of the small claw. 

 At the next moult the small claw becomes the large one, and the 

 new claw the small one. 



As yet no one has detected the nature of the correlation that 

 causes the transposition, and this must obviously be the next step 

 in advance. Wilson has suggested that the throwing over is con- 

 nected with the nervous system, but the experiments on which 

 he bases this suggestion appear to me to be capable also of an- 

 other interpretation. 



During the past summer I undertook some experiments which 

 I hoped would give results bearing on this question, but the out- 

 come has been almost entirely negative. Nevertheless, I shall 

 venture to describe these experiments briefly, because if carried 

 out on more suitable forms they will very probably throw some 

 light on this exceedingly important subject. 



Several years ago I found that by cutting the nerve of the leg 

 of the hermit-crab, proximal to the breaking joint, the leg can 

 then be cut off at any level beyond the breaking joint without the 

 remaining part being thrown off at the base. By removing por- 

 tions of the large leg at different levels, after first cutting the 

 nerve at the base, I hoped to be able to discover whether the 

 amount removed had any effect on the transposition of the large 

 claw to the other side. It was also possible that the simple 

 cutting of the nerve might have some effect, as Wilson's experi- 

 ment seems to show. The result might also, as Wilson appears 

 to believe, depend in part upon the degree to which the new nerve 



1 Roux's Arc/iiv, XIII., 1902. 



2 BIOLOGICAL BULLETIN, IV., 1903. 



