THE MUSCULAR SYSTEM. 



259 



Of parasites are to be noticed the not unfrequent Cysticercus cellulose? 

 and Trichina spiralis ; and, besides these, in the Eel a nematoid worm, 

 observed by Bowman (" Cyclop, of Anat." II. p. 512) alive, in the al- 

 most empty sarcolemma. I met with something analogous to the latter, 

 some years ago, in the abdominal muscles of the Rat (as have V. Sie- 

 bold and Miescher also in the Mouse) ; that is to say white streaks 47 

 lines long, and 0-09-0-01 of a line wide, which, on microscopic exa- 

 mination, proved to be hollow primitive fasciculi, entirely filled with 

 elliptical, slightly curved corpuscles, 0-004 0*005 of a line long, by 

 0-0019 of a line wide, and manifestly ova. The portions of the fas- 

 ciculi thus transformed into pouches, had walls 0-009-0-01 of a line 

 thick, with transverse stripes, and were continuous at either end with 

 the perfectly normal fibre. 



87. Physiological Remarks. The most remarkable peculiarity 

 of the muscles is their contractility. In each contraction, the primitive 

 fasciculi shorten themselves in a rectilinear direction, and at the same 

 time become thicker ; they do not, however, undergo any considerable 

 condensation. It is probable, that the contractions generally take 

 place simultaneously in every part of a fasciculus, although at the same 

 time it is not, of course, intended to be said that the contraction does 

 not commence at the points where the terminations of the nerves occur, 

 and that this contraction does not precede, though by a space of time 

 immeasurably short, or at all events inappreciable by the eye, that of 

 the other portions of the fasciculus. Under certain conditions, how- 

 ever, successive, progressive, and partial contractions are 

 observed. If during the contraction of a muscle, its 

 longitudinal and transverse striae are noticed, it is diffi- 

 cult to show that where the former exist, they disappear 

 during the contraction, and give place to transverse 

 markings ; and that the latter, where they were already 

 present, become more distinct, and more closely approxi- 

 mated. Moreover, in the easily isolated fibrils of the 

 thoracic muscles of insects, it is easy to perceive that 

 they exhibit very variable conditions in different ani- 

 mals, and vary frequently in one and the same indivi- 

 dual. Sometimes they are almost without transverse 

 markings, and very pale ; sometimes darker, and with 

 distinct transverse lines; sometimes, again, very dis- 

 tinctly ringed ; and together with these varying condi- 

 tions, does the thickness of the fibrils and the distance 

 between the transverse striae, vary also ; so that the 



Fig. 108. Primitive fibres from the alar muscles of the " Dung-Fly :" a, slender fibril, 

 with very distant delicate transverse striae ; b, thicker fibre, with closer, alternately stronger and 

 fainter striae; c, still thicker fibril, with the striae more closely approximated; rf, fibril with 

 lateral, alternate elevations (they have come out too dark). Magnified 350 diameters. 



Fig. 108. 



