INFLUENCE OF NERVE ON REGENERATION. 45 



aquarium, so that external conditions could play little, if any, 

 part in the result, an interval of ten days or more might occur 

 between the earliest and latest appearance of proliferation. The 

 results obtained after cutting the nerve at this level may have 

 been due to the presence of collateral nerve-connection sufficient 

 to give the required stimulus to the tissue ; for as was later clearly 

 shown, the nerve is an important factor in the regeneration. 



In the succeeding series the nerve was cut through the pelvic 

 girdle close to the backbone, in the hope of more completely 

 cutting off the nerve supply of the limb. The incision necessarily 

 went through into the body cavity as the nerves given off from 

 the spinal cord lie close to the inner wall and are covered only 

 by ccelomic epithelium. The operation is by no means as serious 

 as would be imagined, since the wound heals completely in three 

 days. During this time the animal acts in a perfectly normal 

 manner except for the injured leg. Instead of using separate 

 individuals for checks as before, both legs of the same individual 

 were amputated, but the nerve was cut on one side only. The 

 males are much more difficult to operate upon than the females, 

 on account of their greater muscular development, whereas in 

 the female the pelvic girdle stands out prominently and the body 

 wall is thin. In the males the girdle is not visible externally and 

 is overlaid by a thick musculature which renders operating upon 

 the animal at this point difficult. 



On November 26 a set of seven salamanders was operated 

 upon as described above. They were not again observed until 

 the forty-fifth day. At that time both legs of each individual 

 had proliferated material to a greater or less extent. The side 

 used as a check could be identified in every case but one, by its 

 far greater amount of proliferated material. 



In the exception the animal assumed a peculiar green color, 

 evidently from a disease, and at a later period both legs were 

 entirely sloughed off. This set was continued under observation 

 until the eighty-third day, at which time there was still a decided 

 difference between the appearance of the two sides, although by 

 no means as pronounced as before. The check showed in each 

 individual the foot plainly differentiated, while in only two in- 

 stances was this the case upon the other side, and even in those 

 cases to a much less extent. 



