Royal Society. 505 



a minuter size ; which in their turn surround others still more mi- 

 nute ; and so on. The outer spirals enter for the most part into the 

 formation of the investing membrane discovered by Schwann, but 

 for the only complete description of which, in a formed state, we are 

 indebted to Mr. Bowman. The inner spirals constitute what are de- 

 nominated tlie fibrUlce. The fibril appears to the author to be no other 

 than a state of the object which he designates s. flat filament ; and 

 which, as he shows, is a compound structure. The fibril he finds to 

 be, not round and beaded, as it has been supposed, but a flat and 

 grooved filament ; the description above given of the structure of the 

 filament being especially applicable here. This flat filament is so 

 situated in the fasciculus of voluntary muscle, as to present its edge 

 to the observer. It seems to have been the appearance presented 

 by the edge of this filament, that is to say, by the curves of a spiral 

 thread, that suggested the idea of longitudinal bead-like enlarge- 

 ments of the fibril, as producing striae in the fasciculus of volun- 

 tary muscle. In the author's opinion, the dark longitudinal striae 

 are spaces (probably occupied by a lubricating fluid) between the 

 edges of flat filaments, each filament being composed of two spiral 

 threads, and the dark transverse striae, rows of spaces between the 

 curves of these spiral threads. The filament now mentioned, or its 

 edge, seems to correspond to the primitive marked thread or cylinder 

 of Fontana — to the primitive fibre of Valentin and Schwann — to the 

 marked filament of Skey — to the elementary fibre of Mandl — to the 

 beaded fibril of Schwann, Miiller, Lauth, and Bowman — and to the 

 granular fibre of Gerber. The changes known to be produced by the 

 alternate shortening and lengthening of a single spiral are exhibited 

 in the microscope by a fasciculus of spirals, not only in its length 

 and thickness, but in the width of the sjjaces (strice) between the 

 curves of the spirals. And a muscle being no other than a vast bundle 

 of spirals, it is in contraction short and thick ; while in relaxation it 

 is long and thin ; and thus there occurs no flattening of bead-like 

 segments in contraction. The author has found no segments that 

 could undergo this change. These observations on the form of the 

 ultimate threads in voluntary muscle, "were first made on the larva 

 of a Batrachian reptile ; and have been confirmed by an examination 

 of this structure in each class of vertebrated animals, as well as in 

 the Crustacea, Mollusca, Annelida, and Insects. 



He finds that the toothed fibre, discovered by Sir David Brewster 

 in the crystalline lens, is formed out of an enlarged filament ; the 

 projecting portions of the spiral threads in the filament, that is, the 

 apparent segments, becoming the teeth of that fibre. 



The compound filaments are seen with peculiar distinctness in the 

 blood-vessels of the arachnoid membrane. In connexion with the 

 spiral direction of the outer filament in these vessels, the author refers 

 to the rouleaux in which the red blood-discs are seen to arrange them- 

 selves, in the microscope, as probably indicating a tendency to pro- 

 duce spiral filaments. To form rouleaux, corpuscle joins itself to 

 corpuscle, that is to say, ring to ring ; and rings pass into coils. 

 The union of such coils, end to end, would form a spiral. But the 

 formation by the blood-corpuscles of these rouleaux is interesting in 



