MUSCLE. 135 
are also elongated m the direction of the fibre. Some 
of the nuclei, those for instance which appear to be placed on 
their edges, may possibly become absorbed at the same time, 
for they never present that position at a later period. The de- 
velopment of the whole cylinder proceeds simultaneously, its 
granulous aspect disappearing, and the small granules of the 
cavity also diminishing in quantity. All the stages of transi- 
tion from the second form into that first described may be 
observed. The extension does not appear to take place quite 
regularly, but may be stronger at particular parts, so that, 
for a considerable extent, a fibre may be somewhat narrow, 
and present no nucleus, and then again an intumescence oc- 
curs in which a nucleus lies. 
It now, however, becomes a question how the form of mus- 
cular fibre last described is generated, and what its elementary 
form may be. It presented a cylinder, which is most probably 
hollow, and may be presumed to be closed at both ends, since 
the muscular fibres terminate abruptly at the tendons, with a 
well-defined and bluntly-rounded extremity. Cell-nuclei le 
within this cylinder at very small distances from one another. 
Is the cylinder an elongated cell, in which nuclei are formed 
as the rudiments of new cells, which, however, are not deve- 
loped; or are the nuclei the remains of cells, which, by coales- 
cence with one another and absorption of the septa, form the 
entire fibre or cylinder? Or, in other words, is the fibre 
generated by a coalescence of cells ? 
I have not observed the stages of transition m which 
original cells arranged themselves in a linear series to form a 
fibre, the recent embryos at my command not being sufficiently 
young for the purpose. I have, indeed, met with an appear- 
ance in the form of muscular fibre last described, which might 
be regarded as an indication that those fibres are composed of 
small portions joined together. Their margins were incur- 
vated at different spots, and a line, indicative of a division, ran 
transversely across the entire thickness of the fibre. I have 
endeavoured to delineate this appearance in pl. IV, fig. 1, d, 
but I have not succeeded in representing its true character, 
and it was not, in itself, conclusive. There are some other argu- 
ments in favour of the fibre of muscle being composed of sepa- 
rate particles. Many of the muscles of fishes or tadpoles, for 
