MUSCULAR TISSUE. 



cleave across in a direction parallel to these stripes, and even break up into 

 tranverse plates or disks, which are formed by the lateral cohesion of the 

 particles of adjacent fibrils. To make up such a disk, therefore, every fibril 

 contributes a particle, which separates from those of its own fibril, but co- 

 heres with its neigh- 

 Fig. LXIII. bour on each side, 



and this with per- 

 fect regularity. In* 

 deed, Mr. Bowman 

 conceives that the 

 subdivision of a fibre 

 into fibrillae is 

 merely a phenome- 

 non of the same 

 kind, only of more 

 common occurrence, 

 the cleavage in the 

 latter case taking 

 place longitudinally 

 instead of trans- 



Fig. LXIV. 



Fig. LXIII. 

 MUSCULAR 



A. PORTION OF A (RATHER SMALL SIZED) 

 FIBRE, PROM A WATER BEETLE, MAGNIFIED 



imimiiiiiiii 

 limimiimii 

 iiimmmiiii 

 ijiiiiiiiiiiiii 

 ijiiiiiiiuiml 

 iiiiiiiiiiiiiii 



730 DIAMETERS. 



rt, a, dark cross bands formed by the apposition of slender 

 rod-shaped sarcous elements ; b, b, light stripes with inter- 

 mediate line of dark specks; at a' , of, inclined position of rods, 

 as here and there seen. B, a detached bundle of fibrils 

 equally magnified. On one side an apparently single series of 

 elongated sarcous elements, with intermediate dots, possibly a 

 single fibril. 



Fig. LXIV. DIAGRAM 

 TO SHOW HOW THK 

 STRIPES OF MUSCU- 

 LAR FIBRE ARE PRO- 

 DUCED. 



versely : according- 

 ly, he considers that 

 the fibrillse have no 

 existence as such in the fibre, any more than the disks ; but that both the 

 one and the other owe their origin to the regular arrangement of the 

 particles of the fibre longitudinally and transversely, whereby, on the appli- 

 cation of a severing force, it cleaves in the one or in the other direction into 

 regular segments. 



While some consider that the fibrils are composed throughout of the same substance, 

 and that the alternation of dark and light portions is due to unimportant modifica- 

 tions of it, others believe that the light and dark parts differ essentially in nature. 

 In proof of this Briicke adduces observations to show that the dark parts, or sarcous 

 elements, doubly refract the light (or are " anisotropic "), whilst the intermediate 

 light substance is singly refractive (" isotropic"). Moreover, as the sarcous elements 

 and the dark stripes formed by them are variable in size and position the stripes 

 being sometimes broad and widely apart, at other times narrow and closer together 

 Briicke infers that the dark, doubly refracting, or anisotropic substance consists of an 

 aggregation of undistinguishably minute, doubly refracting molecules, named by him 

 disdiaclasts, imbedded in the isotropic matter; which, by grouping together in 

 various numbers and modes, give rise to the variations in the size, figure, and arrange- 

 ment of the sarcous elements. In reference to this view I may observe that, while it 



