150 Victor E. Emmel. 
ogenous plates or tendons for each of the eight muscles distal of 
the breaking joint were found to be differentiated in the following 
order: (1) for the flexor muscle in the second limb segment; (2) the 
flexor in the third segment, together with the extensor in the second 
segment; (3) the flexor in the third segment, and at the same time 
the two extensors in the fifth segment; (4) and last, the extensor in 
the third segment. From these results it seems evident that the 
direction of differentiation cannot be described as being any more a 
disto-proximal one than the reverse. The important point disclosed 
is that in each segment the tendon for the flexor, or larger muscle 
of the pair, is differentiated first; and further, of these flexors the 
larger ones are the first to develop. 
2. Differentiation of Myofibrilla.—The results of the microscop- 
ical study of the earliest differentiation of the myofibrille in each 
pair of regenerating muscles are presented in the following table. In 
this table the first column gives the time of regeneration. The signs 
++ and 0 indicate, respectively, the presence or absence of myofibrils. 
TABLE SHOWING THE SEQUENCE OF DIFFERENTIATION OF MYOFIBRILLAE IN HACH 
OF THE EHicHTt LIMB MUSCLES DISTAL TO THE BREAKING JOINT. 
Series Second Segment.| Third Segment. Fourth Segment.) Fifth Segment. 
Regeneration. | 
No. Flex. Exten. Flex. Exten. Flex. Exten. Exten. Exten 
29 5 da. 9 hrs ar 0 0 0 0 0 0 
30 | 5 da. 10 hrs + 0 0 +* 0 0 
31 5 da. 22 hrs. + + + +* + +%* 0 0 
3a sG.das Guhirs: +oo+ + + + + + + 
*Differentiation just beginning. 
In this table it will be seen that the first muscle fibrils to be differ- 
entiated were those of the flexor in the second segment; the next to 
appear were those of the flexor in the fourth segment. Up to this 
time no muscle fibrillse were found in either the third segment or 
in the extensors in the second and fourth segments. The flexors in 
the fifth segment were the last to develop. Here again, differentia- 
