296 



TOWLE. 



[VOL. II. 



One further point should be mentioned. In stage 5 the 

 line of distinction between new and old fibers is clear, owing 

 to their difference in size. In stage 7 this distinction has 

 disappeared. This is due not only to an increase in the size 

 of the new fibers, but to a decrease in the old. This decrease 

 is, I believe, due to the longitudinal splitting of such of the old 

 fibers as are left (Fig. /. a and b}. 



Beside the stages described above, four others were preserved 

 and cut longitudinally. This was a somewhat difficult opera- 

 tion, for the new part forms at 

 an angle with the upper arm, 

 and it is hard to orient the 

 piece in such a way as to insure 



FIG. 7 a. 



FIG. i b. 



true longitudinal cutting of the muscle fibers. The material 

 was preserved at the following intervals : 



Time of Operation. 



i. Jan. 29, 1900. 



-. .. 4 i .. 



-) t. 



4. 



Time of Killing. 



Feb. 2, 1900. 



Age of Stump. 



4 days. 

 14 



21 " 

 3 " 



The first of these shows no transformation at the cut ends 

 of the muscles, but the ectoderm has closed in over the wound. 

 In the second there is a considerable increase in the thickness 

 of the ectoderm, and under it a collection of scattered nuclei, 

 exactly similar to the tissue in the growing end of later stages. 

 As the limb grows in length this tissue increases in amount 

 and a number of mitoses are seen in it. Degeneration of the 

 old fibers is distinctly noticeable in stage 3, and fibers are 

 found, as before, filled with nuclei, but there is no karyokinesis 

 in any muscle fiber. 



