Tissues in the Crustacean Limb. 151 
tion does not proceed definitely in either a proximal or a distal 
direction, but appears rather to be correlated with the size and fune- 
tion of the muscles concerned. 
3. Differentiation of Striw in the Myofibrille.—The series were 
also studied to ascertain the time at which myofibrils in each muscle 
showed striations. The following table represents the results ob- 
tained. The signs + and 0 indicate, respectively, the presence and 
absence of striation. 
TABLE SHOWING THE SEQUENCE IN THE DIFFERENTIATION OF STRIAE IN THE 
REGENERATING Limp MUSCLES. 
Series Second Segment. Third Segment. |Fourth Segment. Fifth Segment. 
Regeneration. 
No Flex. Exten. | Flex. Exten. | Flex. Exten. | Exten. Exten. 
34 6 da. 22 hrs. +%* + 0 0 
35 |7da. 2 hrs. | oL ea eee + + Se Sap + if 
*Striations were not found until after the myofibrillz had begun to be 
differentiated in all the segments. 
{Differentiation of strise just becoming evident. 
The time intervening between the appearance of the first stris 
and the striation of all the muscles is apparently much shorter than 
the time between the first differentiation of myofibrils and their 
complete development for all the muscles. N evertheless, striation 
does not occur simultaneously throughout the limb. The strie differ- 
entiate first in the flexor museles in the second and fourth segments, 
and later they appear in the remaining limb muscles. 
4. Conclusions.—The results of the present study of the differen- 
tiation of the chitinogenous muscle tendons, the myofibrille and their 
striation justify two conclusions: 
First, that the differentiation of the regenerating musculature 
proceeds in neither a definite disto-proximal direction, nor the 
reverse. 
Second, that whatever sequence there may be in this differentia- 
tion is correlated rather with the size and functional relations of the 
various muscles concerned, the larger muscles differentiating first. 
