Eoss Granville Harrison 



307 



^ 



^ 



^1 f 



i 



Fig. 9. 



il 



entirely gone from the myotomes and the fibers are crowded with striated 

 fibrillar (Fig. 9). The most striking abnormal feature in the individual 

 under consideration is the presence of 



vacuoles in the axes of the muscle fibers, ^, 



together with a larger amount of pigment nlSi 



than is usually found. The muscle cells 

 of normal larvce may, however, show some 

 vacuolization in the axial protoplasm at 

 the time when the absorption of the yolk 

 is about completed. In the injured larva 

 the length of the muscle fibers is not so 

 great as in the normal; many fibers are 

 separated from the neighboring ones by 

 clear spaces. Cross sections of a larva 

 of the same age as the one just described 

 show that the muscle fibers are sur- 

 rounded by a very delicate membrane, 

 the sarcolemma (Fig. 11). The fibers, 

 which are cut near the end, are filled out 

 entirely by fibrillse; those cut near the 

 middle show nuclei mostly situated in the 

 axis of the fiber, though sometimes ec- 

 centrically placed just beneath the sar- 

 colemma. Vacuoles are also present in 

 the axial sarcoplasm. 



The amount of vacuolization shown by 

 the muscle fibers varies considerably in 

 different specimens and even in different 

 regions of the same one. Thus, there are 

 often to be found fibers of perfectly 

 normal appearance, with no vacuoles at 

 all and no other signs of degeneration. 

 Such a fiber, taken from the tail of an 

 individual much like the one shown in 

 Fig. 6,. is shown in the accompanying cut 

 (Fig. 10). In the musculature of the 

 limb of the specimen described in the 

 next section there are likewise no vacuoles 

 in the fibers. On the other hand, in some 



specimens there is not only marked vacuolization, but also alteration of 

 the contractile substance and partial arrest of its development. Blotches 



'km 



Fig. 10. 



Fig. 9. Two muscle tibers from the 

 root of the tail of a larva from which 

 the spinal cord had been removed six 

 days prior to ttxation ; v. vacuole ; y, 

 yolk spherule. 



Fig. 10. Muscle tiber from tail of 

 larva similar to the one shown in Fig-. 

 6. Killed seven days after cutting: 

 the spinal coi-d. This figure has been 

 reduced to the size of Fig. 9 for com- 

 parison, thoug-h the magnification is 

 much greater. 



