AUTOTOMY OF THE TAIL IN RODENTS. 3 



itself. The possibility of a regeneration of the missing part of 

 the tail was tested in fourteen specimens. Some of these under- 

 went a voluntary autotomy, in the manner above described. 

 In others, the breaking of the appendage was facilitated by the 

 observer. These mice were all nearly mature, though probably 

 most of them had not reached the limit of growth. 



In the first seven specimens, the stump of the tail was measured 

 shortly after the operation, but the length of the body was 

 unfortunately not taken. Four of these specimens were living 

 at the end of twelve months. In three cases, the tail has under- 

 gone a slight elongation (1-5 mm.), but this was doubtless 

 merely an ordinary process of growth, accompanying the general 

 growth of the body. In the fourth case, the recorded growth 

 was 1 8 mm , though we believe this to be based upon an error 

 in the first measurement. Except for the hair conditions, to be 

 described below, there was no evidence of restoration of any 

 part of the tail. 



The next seven specimens were dealt with much more care- 

 fully. The length of the detached portion of the appendage 

 was determined; likewise that of the stump, and the length of 

 the body from the snout to the base of the tail. 1 Six of this 

 second lot of mice were living at the end of nine months. When 

 measured then, it was found that the tail stumps in five specimens 

 had undergone a trivial increase in length, averaging about two 

 millimeters. This was evidently incidental to a slight general 

 growth of the body, since the mean body length, during the 

 interval, had increased about four millimeters. In the sixth 

 specimen, the tail was actually shorter, its condition indicating 

 that it had been further damaged after the original operation. 



Examination of the tissues of the tail in all of the foregoing 

 specimens gave no suggestion of regenerative processes. In each 

 case, the vertebral column terminated in a partial vertebra, this 

 being evidently the one which was fractured in the process of 

 autotomy. 



There was, however, one very interesting result. In most of 

 the specimens a dense tuft of elongated hairs had formed at the 

 termination of the stump, the solid core of the latter being in 



1 In making the latter measurements the animal was etherized. 



