582 



Comparative Animal Physiology 



widths of A to I bands approaches 1 in faster muscles and is much less 

 than 1 in slower muscles.^^ In crabs the striation widths exceed 10 fi but 

 tend to be narrower in the faster muscles of a given individuals^® The 

 contractile proteins are distributed throughout the. fiber, hence the material 

 of the striations is not concerned directly with contraction, and there is no 

 clear explanation of why striated muscle is faster than non-striated. 



D 



B 



■3 iy 





Vi 





Anisotropic band 



Isotropic band 



Sarcolennma 



-- » v " w » 



«i»"«4 !fPl W"i W"*" 



MV."' ' - !r"i Vi ' - ' 



u ,.. ., Nucleus I 



Tonus fibrils I 



Fig. 217. Views of muscle fibers: fibers of longitudinal retractor muscles of Thy one: 

 longitudinal sections, A, in relaxed, and B, in contracted state; C, cross section in relaxed 

 state. No striations, no fibrils, much connective tissue. Olson."^ D, Portion of muscle 

 fiber from heart of Ciona. Striated on one side, non-striated on other side. Bozler." 



Muscle striations are usually less sharp in vertebrates than in arthropods, 

 sarcomere lengths are usually 2-3 jx, and in isotonic contraction they may 

 sometimes be reduced to half this length. In amniotes and in some fish, 

 striated muscle may be white or red. The color is less important than are 

 other characters; in white muscle the fibrils are close together and abun- 



