PKOGRESS OF MICROSCOPICAL SCIENCE. 125 



of the trunk of some species of Trombidium, are remarkable for the 

 extraordinarily large distance of their transverse stri^, this being 

 from ten to three raicromillimetres. If the whole animal be placed 

 for one or two hours in a solution containing 1 per cent, of perosmic 

 acid, and, after having been washed in water, be dissected in diluted 

 glycerine, the striped muscular fibres are seen under the microscope 

 to have become stained by that reagent very dijSerently in their dif- 

 ferent parts. First of all, the whole fibre is seen to be divided by 

 transverse membranes or septa, continuous with the sarcolemma. 

 Each division contains in its central region an anisotropous trans- 

 verse disk, which appears to consist of a matrix slightly stained with 

 perosmic acid ; in it are imbedded rods which are stained readily 

 by that reagent. In many cases, the transverse disk appears to be 

 divided into two by a very slightly stained median layer, which 

 probably corresponds to the median disk of Hensen. Each division 

 also contains, between the above-mentioned transverse disk and the 

 transverse membrane, an isotropous transparent disk, not at all stained 

 by perosmic acid. This contains, more or less near to the transverse 

 membrane, a row of granules of equal diameter, each of which repre- 

 sents the continuation of a rod of the transverse disk above men- 

 tioned ; this row of granules is the granular layer of Flogel. 



Besides these typical appearances of muscular fibres with broad 

 striation, there are other fibres in which the transverse strife are much 

 narrower. On comparing these with the former, it is seen that the 

 narrower the striation the more indistinct the median layer becomes, 

 until finally it disappears completely, so that then the transverse disk 

 consists of continuous rods; further, that at the same time the 

 granular layer approaches the transverse membrane to such a degree, 

 that they can hardly be distinguished as two different structures. 

 Consequently the muscular fibres with narrow striation present the 

 appearances commonly described, viz. a dim anisotropous disk ; on 

 each side of its short diameter (namely, that corresponding to the 

 longitudinal diameter of the muscular fibre) a transparent bright 

 layer : and finally, the bordering transverse membrane. 



In polarized light (strong light and a magnifying power of 1000 

 being used) it is evident that, besides the sarcolemma and the trans- 

 verse membrane, only the rods of the transverse disk and the rod- 

 granules of the granular layer are doubly refractive, whereas all other 

 parts are isotropous. From this it may be deduced that each muscular 

 division is filled with an isotropous transparent matrix, in which are 

 imbedded anisotropous rods ; to each of these belongs at each extremity 

 an anisotropous granule. In preparations made with perosmic acid, 

 bundles of muscular fibres are not unfrequently met with, which, 

 being fixed at one side by their insertion to the skin, show at the 

 same distance from that insertion a fusiform swelling. This on close 

 observation corresponds to a contraction-wave, rendered permanent 

 by the perosmic acid. In such swellings, it is seen that the gra- 

 nular layer and the isotropous disk on each side of the transverse 

 membrane have, together with this latter, become reduced to one 

 broad layer which is even darker than the anisotropous transverse 



