Striped Muscular Fiber of a Beetle
Part of a striped muscle fiber of a water beetle prepared with absolute alcohol. Labels: A, sarcolemma; B, Krause’s membrane. The sarcolemma shows regular bulgings. Above and below Krause’s membrane are seen the transparent “lateral discs". The chief mass of a muscular compartment is occupied by the contractile disc composed of sarcous elements. The substance of the individual sarcous elements has collected more at the extremity than in the center: hence this latter is ore transparent. The optical effect of this is that the contractile disc appears to posses a “median disc” (Disc of Hensen). Several nuclei of muscle corpuscles, C and D, are shown, and in them a minute network.
Baker, W. Morrant & Harris, Vincent Dormer Kirkes' Hand-book of Physiology, 13th ed. (Philadelphia: P. Blakiston's Son & Co., 1892) 88