104 DE. WILSON FOX ON THE DEVELOPMENT 



profile), and separated from it by a distinct space which is filled with the same granular 

 and pigmentary matter as that which occupies the portion of the cell which is free 

 from striation, and which may be seen, on altering the focus, to be difiused, but much 

 less thickly, over the surface of the striated part ; so that, to my own mind, the conclusion 

 is unavoidable, that the membrane, which can be thus distinctly seen in profile at the 

 edges of the fibres, encloses a space occupied (1) by one or more nuclei, (2) by a 

 substance striated both longitudinally and transversely, and (3) by amorphous trans- 

 parent matter containing suspended in it a varying amount of granules and pigment. 

 Sometimes a nucleus may be seen on each side of the striated portion, in which case 

 the membrane and gi'anular contents can be seen to extend continuously over the whole 

 structure (see Plate V. fig. 13). 



In some cases, when a muscle-cell at an early stage of its development contains two or 

 more nuclei, it shows a tendency to division, which is evidenced by an imperfect con- 

 striction between the nuclei, this constriction being apparent on that side only of the cell 

 which contains the nuclei, and not affecting the striated portion, if the latter change has 

 already made its appearance within the cell. At later stages, when the fibre has become 

 more elongated, and the nuclei are further removed from each other, there is always a 

 depression in the outline of the membrane between the nuclei, and this may sometimes 

 proceed to a considerable depth, but never, as far as I have observed, to a complete con- 

 striction and separation between the difierent nuclei (see Plate V. figs. 9, 10, 14, 16). 



There is a considerable difierence in the number of the nuclei contained within the 

 membrane. They may sometimes be very numerous, and the breadth of the fibre is 

 usually proportioned to the number of the nuclei. At other times a long cell may contain 

 only two or three nuclei ; and the difference appears to depend on the multiplication of 

 the nuclei occurring at variable periods in the development of the fibre. Thus figs. 8, 

 9, 10, and 17 illustrate progressive stages of this process in those rarer cases in which 

 the nuclei are found lying across the long diameter of the fibre; while figs. 7, 11, 12, 

 14, and 16 are instances of fibres, or portions of fibres where many nuclei exist within 

 the membrane. 



On the other hand, during the early stages of development, instances are found, with 

 even greater frequency, in which a very long fibre, much narrower than the others, has 

 only a single nucleus attached to it throughout its whole course (Plate V. figs. 18 &; 19 

 represent front and profile views of this condition). With a high magnifying power it 

 may in these cases be distinctly seen that a delicate membrane, often separated somewhat 

 from the nucleus by granular contents, limits the outline of the fibre, on which its pro- 

 longation can often be traced to some little distance from the nucleus. 



These fibres often lie imbricated closely together, and in their earlier stages they may 

 often be seen presenting a spindle-shaped appearance (like Plate V. figs. 24 & 26, from 

 the Chick) ; by which I think that the inference is further justified that these fibres may 

 be regarded as having been produced by the continuous elongation of cells such as are 



