The Interstitial Granules of Striated Muscle etc. 311 



that the granules lie mainly in the isotropic band, or that they are at 

 least most readily visible there. In Kölliker's figures of the wing 

 muscle fibers of insects it is apparent that the granules correspond in 

 position to the anisotropic segment, tho the author does not call atten- 

 tion to this relation. Arnold describes the glycogen-holding granules in 

 the skeletal muscles of the frog in the isotropic segment — J-granules, 

 He figures the glycogen as extending thru the anisotropic segment 

 when a large quantity is present. 



Holmgren (1910, S. 306) states that in the wing muscles of insects 

 and in the heart muscle of crustaceans and mammals the interstitial 

 granules correspond in position to the anisotropic segment ( Q-granules) ; 

 but that in the skeletal muscles of insects and in general also in those of 

 mammals they lie in the isotropic segment (J-granules). A number 

 of observers have noted that the granules are sometimes arranged in 

 transverse as well as in longitudinal rows. 



It is easy to verify Holmgren's observation on the wing muscles 

 of insects. In the moth (Phlegethontius) and the fly (Musca), in June 

 at least, it can readily be seen even in unstained preparations that the 

 large granules occupy the Q-band; but in other muscles it is often 

 difficult to determine the position of the granules. In the skeletal 

 muscles of vertebrates', when the cross markings are wide and distinct, 

 it can usually be seen that the granules occupy the J-band. But when 

 the striations are narrow the granules seem to extend the entire distance 

 between adjacent Krause's membranes. Large granules nearly always 

 lie partly at least in the Q-band. In many fibers the granules are 

 arranged in distinct transverse rows, being apparently limited by 

 Krause's membrane. I have not been able to determine the position of 

 the granules in cardiac muscle. 



It will be pointed out farther on that the large Q-granules of 

 insect muscle are chemically different from the granules of vertebrate 

 muscle; but the observations are too few to warrant any general state- 

 ment as to whether there are fundamentally any differences between 

 Q-granules and J-granules. 



Chemical composition of the interstitial granules. The observations 

 of the various authors on this topic have been given in the review of the 



