6 CLARKE, ON STRIPED MUSCULAR FIBRE. 
between the latter increase the bands which separated them 
fall in and coalesce, so that the diameters of the fibres 
decrease. Soon after the nuclei have separated some of 
them begin to decay by breaking up into irregular clusters of 
granules, which themselves soon disappear. At this period 
the strize first become visible within the margin of the fibre, 
and then pass gradually towards the centre. The fibres now 
begin to increase in size by means of the surrounding cyto- 
blasts. These become attached to their exterior, and invested 
by blastema, which generally forms a continuous layer be- 
tween them. The nuclei subsequently sink into the sub- 
stance of the fibre, and an ill-defined elevation, which soon 
disappears, is all that remains. 
Now, while this account and that which I have given as the 
result of my own investigations differ from each other in 
many particular points, they still very nearly coincide in 
regard to the general principle or plan upon which the fibres 
originate in the blastema. In the first stage of their forma- 
tion, however, the nuclei are far from bemg always aggre- 
gated in clusters, or even in contact with each other in linear 
series, as may be seen in birds, mammalia, and especially in 
man, in whom such an arrangement never occurs (figs. 4, 
5, 14, and 18); and even when they are in contact or overlay 
each other their adhesion always takes place by means of a 
certain quantity of blastema, as at e¢, figs. 5, 6, and 14. 
When they are at some distance from each other, the blas- 
tema which cements them in a larger or smaller quantity is 
more or less enclosed as an axis by the condensed substance 
of the lateral bands, and contributes to the extension of these 
bands or to the formation of separate fibrillee around the rest 
of the fibre, which, however, mcreases in diameter by the 
deposition of fresh material on its surface (fig. 4 a, b, ¢; 
fig. 5 a, 6, d.) In many instances, particularly in the 
younger fibres, the nuclei are crowded together in close con- 
tact, as represented by Savory, and sometimes they overlap 
each other, as represented at c, fig. 5. When several of them 
are compressed closely together they frequently seem as if 
they were undergoing a process of division, and such a pro- 
cess does actually take place in many instances within the 
fibres, where the nuclei frequently occur in pairs or in rows 
of three or four. 
My observations on the first stage of development of mus- 
cular fibre in the Auman foetus, with many of the drawings, were 
made at the beginning of the present year (1861). Those in 
the chick I made in the following June and July; and while 
occupied with the same subject in mammalia during the 
