112 



MUSCULAR TISSUE. 



in the latter case taking place longitudinally instead of transversely : 

 accordingly, he considers that the fibrilhB 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 (sarcous elements) longitudinally and transversely, whereby, 

 on the application of a severing force, it cleaves in the one or in tlie 

 other direction into regular segments. Kolliker, on the other hand, 

 holds to the opinion that the fibrils pre-exist as such, and that they 

 are of essentially the same nature from end to end of the fibre, the 

 alternating dark and light parts being due to diflFerences in optical 

 characters merely : he describes them as being collected into definite 

 bundles (which make up a fibre), termed by him " muscle-columns." 



It is difficult, however, on account of the extreme delicacy of the 

 elements composing it and the readiness with whicli changes occur in 

 them, to make out, with the means at present at our command, the 

 exact structure of the mammalian muscular fibre ; and, to endeavour 

 to attain to a satisfactory knowledge of the subject, histologists have 

 therefore largely availed themselves of the facilities aflJbrded by 

 the muscular fibres of the arthropoda, and especially of the water- 

 beetle, which are quite similar in appearance and character, but in 

 which the elements are relatively large, these fibres, moreover, are 

 readily obtained in a perfectly unaltered and still contractile condition. 

 Such muscular fibres, when examined, without the addition of any 

 fluid, under a high power of the microscope, in what may be considered 

 their typical condition, present, like mammalian muscle, the appear- 

 ance of alternate dim and bright stripes crossing the fibre. Each 

 dim stripe is seen to be pervaded by a series of minute rod-shaped 



particles set side by side, with their 

 axes parallel to that of the fibre (fig. 

 68). Crossing tlie fibre in the middle 

 of each of the bright stripes a double 

 row of dots (c) is apparent ; and 

 on close inspection it may be seen 

 that each rod-shaped particle of the 

 dim stripe is traceable at each end 

 into one of the dots of the bright 

 stripe : the dots consequently are 

 merely the knobbed ends of the rod- 

 shaped particles. In this way the 

 whole fibre is pervaded by these 

 minute rods (muscle-rods, d ). The 

 muscle-rods refract the light more 

 strongly than the rest of the mus- 

 cular substance, and hence appear 

 somewhat darker; like that sub- 

 stance, they are probably of a soft 

 and yielding nature. 



Now it can be shown that a linear 

 series of strongly refracting sphe- 

 roids, like the enlarged ends of the 

 muscle-rods, must necessarily have 

 the effect, when viewed by trans- 

 bright band, due to diffraction, on 



Fig. 68. 



Fig. 68.— Living Muscle of "Watkr- 



BEETLE (DyTISCUS MARGINALIS), 



HIGHLY MAGXIFIED. 



s, sarcolemma ; «, dim stripe ; b, 

 bright stripe ; c, rows of clots in briglit 

 stripe which are seen to be the knobbed 

 heads of d, iimscle rods. 



mitted light, of producing a 



