194 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 



taken place the muscular fibre presents the appearance of a 

 transverse striation, viz. dim bands alternating with bright 

 ones. The former correspond to the dim shafts of the rods, 

 whereas the latter are due to an optical effect, produced by 

 the presence of the globular heads of the rods, which have a 

 different refraction-index from that of the ground-substance. 

 In this case the muscle-rods are so arranged that the heads 

 of two successive series meet in the middle of the bright 

 band ; when the muscular fibre is somewhat extended the 

 bright band appears to be double, for then the heads of two 

 successive series of rods have become separated, and each 

 series of heads possesses its own halo. During contraction 

 the heads of the rods become enlarged at the expense of the 

 shafts, and at the same time they approach each other in the 

 transverse as well as in the longitudinal direction to such an 

 extent that they form one dark transverse band with bright 

 borders. As the contraction proceeds, and the dark bands 

 approach each other, the bright borders encroach upon the dim 

 stripe, which finally disappears, its place being taken up by 

 a single transverse bright band. The contracted muscular 

 fibre shows, therefore, alternate dark and bright bands, the 

 latter representing merely the ground-substance, which has 

 become accumulated between the shafts of the muscle-rods. 

 In polarized light these bright bands are seen to be aniso- 

 tropous, whereas the dark bands are isotropous. From this 

 it is evident that the ground-substance is anisotropous, the 

 muscle-rods isotropous, although in the state of rest the whole 

 fibre appears to be anisotropous ; this, however, may be easily 

 explained by bearing in mind that the muscle-rods are sur- 

 rounded by the anisotropous ground-substance and are there- 

 fore illuminated by light that has previously traversed this. 



" S chafer is inclined to assume that the ground-substance 

 is comparable to a protoplasmic matrix, which is the true 

 contractile part, whereas the rods are elastic structures, which 

 serve merely to restore the muscular fibre to its original length 

 after the contraction has ceased." 



2. Termination of nerves in voluntary muscle. — Arndt 

 (' Schultze's Archiv,' ix, 481) publishes a long and elaborate 

 memoir on this subject, illustrated with three plates, which 

 our space does not permit us fully to notice. 



3. Petrowsky (' Centralblatt,' No. 49, 1873, p. 769) has 

 studied the growth of muscular fibres in the frog. 



VII. Nervous System. — 1. Nervous structures in general. — 

 Axel Key and Retzius (' Schultze's Archiv,' 1873, ix, pp. 308 

 — 368, 3 plates) publish a long memoir, translated from a 

 Norwegian journal, on the anatomy of the nervous system. 



