110 



MUSCULAK TISSUE 



called 'red' muscle. The former variety, for example the biceps muscle, 

 acts more energetically but is more easily fatigued ; the latter, like the 



muscles of mastication, respiration, the eyeball, and 

 cardiac muscle, are functionally characterized by 

 slower activity but less ready fatigue. The intersti- 

 tial granules accordingly seem to be of nutritive sig- 

 nificance. They are generally more abundant in the 

 J than in the Q segments. The J granules are of 

 spherical form and smaller than the oval Q granules. 

 Striped muscle fibers contain also a trophospongium 

 (Holmgren). Adult muscle cannot regenerate, but is 

 replaced by scar tissue. A young fiber is said to be 

 able to regenerate, the process involving movement of 

 proliferating nuclei toward the cut surface. Muscle 

 growth, as with exercise, depends upon enlargement 





IHUlH 



FIG. 124. S T R i A T E D 

 FIBER FROM A LEG 

 MUSCLE OF THE SEA 

 SPIDER (ANAPODAC- 

 T Y L u s MAXILLARE), 

 SHOWING THE COM- 

 PLEXLY STRIPED CON- 

 DITION CHARACTER- 

 ISTIC OF INSECT MUS- 

 CLE. 



Q, anisotropic disk; J, 

 iso tropic disk; M, mem- 

 brane of H e i d e n h a i n 

 (m eso phr ag ma) ; Z, 

 membrane of Krause (telo- 

 phragma) ; H, median disk 

 of Hensen; N, accessory 

 disk of Merkel; E, terminal 

 disk of Engelmann. X 

 1000. 



ZJQJZJQJZJQJZ 



B 



FIG. 125. SEMIDIAGRAMMATIC DRAWING, REP- 

 RESENTING THE APPEARANCE OF THE SAME 

 FIBER FROM THE LEG MUSCLE OF A BEETLE IN 

 ORDINARY AND POLARIZED LIGHT. 



A, appearance in ordinary light; B, appearance 

 in polarized light. (After Meigs.) 



of the muscle fiber, consequent upon a multiplication of fibrillge by process 

 of longitudinal splitting, and their individual enlargement. 



