on the Structure of the Muscular FibriL 367 



Those drawings show spirals to arise out of piles of particles 

 having a ring-like form. The rings were met with and repre- 

 sented arranged in three ways, viz. 1st, in a single pile, as in 

 fig. 6 A ; 2nd, arranged in alternate or overlapping order, as in 

 fig. 6 B ; 3rd, connected like links of a chain, as in fig. 6 C. 

 Kings arranged in all these ways were found in piles ; and rings 

 arranged in all these ways were seen passing into spirals*. I 

 further showed the existence of such bodies as that in fig #> 6 D f, 

 an altered ring, which if produced must pass into some form of 

 spiral. When each ring of the first arrangement, A, assumes 

 the form D, union of the extremities of a pile of bodies such as 

 D forms a single spiral, and this by longitudinal division passes 

 into two, as in fig. 6EJ. When, according to the second ar- 

 rangement, the rings overlap each other, as in fig. 6 B, or, 

 according to the third arrangement, are connected, as at C, the 

 union of the extremities of a pile of such bodies as that at D is 

 attended with interlacement, forming at once the twin spiral E. 



[Of this twin spiral a drawing from nature (Heart of Frog) is 

 seen in fig. 7. It represents neither full contraction nor com- 

 plete relaxation, but four intermediate states ; and these were 

 seen at different parts of the same fibril. As the two spirals run 

 in the same direction, i. e. as they are parallel, I have been 

 accustomed latterly to term this fibril, and indeed all organic 

 fibre, a twin spiral §. — In all three of the arrangements I showed 

 the rings to have become segmented, as in fig. 7-| b, an appear- 

 ance of course familiar to all accustomed to examine the elements 

 of tissues. The segments intimate the formation of the particles 

 of which spirals are composed ||. — The pellucid centres of the rings 

 are left as elements of future offspring, to assume the form of 

 spirals when their progenitors the old spirals as contractors are 

 worn out.] 



What has just been referred to as seen of the mode of origin 

 of the muscular fibril, I would now apply in considering its 

 mode of reproduction. 



Thus the flat particles in fig. 4 a I apprehend to be in a state 

 resembling or approaching that of rings. They are, in fact, 



* Phil. Trans. 1842, plates 6 and 7, figs. 31-33, 47, 48. 



f Phil. Trans. 1842, plates 5, 6 and 11, many figures. 



X Fig. 6 E represents an apparatus for constructing a model of the twin 

 spiral muscular fibril, to be explained further on. 



§ I had previously called it a double spiral ; but this seems not so fully 

 to imply that the direction of the two spirals is the same. [Originally I 

 believed their directions to be different, but corrected the error in Muller's 

 Archiv for 1850, and in the Phil. Mag. for 1852.] 



|| Phil. Trans. 1842, plate 10, fig. 125. I also showed, by the action of 

 acetic acid, that spiral filaments are made up of particles. (Phil. Trans. 

 1842, plate 8, fig. 68.) 



