110 



MUSCULAE 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 



-N 



FlG. 124. S T R I A T E D 



FIBER FROM A LEG 

 MUSCLE OF THE SEA 

 SPIDER (ANOPLO- 

 DACTYLUS LENTUS), 

 SHOWING THE COM- 

 PLEXLY STRIPED CON- 

 DITION CHARACTER- 

 ISTIC OF INSECT MUS- 

 CLE. 



Q, anisotropic disk; J, 

 isotropic disk; M, mem- 

 brane of Heidenhain 

 (mesophragma); Z, 

 membrane of Krause (telo- 

 phragma) ; H, median disk 

 of Hensen; N, accessory 

 disk of Engelmann; E, 

 terminal disk of Merkel. 

 X 1000. 



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 fibrillse by process 

 of longitudinal splitting, and their individual enlargement. 



