514 



number of coins, and are cemented together by a common layer of 

 blastema. 



In the early part of the seventh day of incubation, numerous fibres 

 of a much larger and more striking description suddenly make their 

 appearance in the nucleated blastema. They originate, however, on 

 the same general plan as the others, in a fibrillation of the blastema 

 between, or along the sides of, a variable number of nuclei ; but the 

 process goes on to form aggregate masses of a much larger kind, and 

 of a more or less oval, fusiform, or cylindrical shape, in which the 

 nuclei are ultimately enclosed. Some of these bodies have a very 

 striking resemblance to organic muscular-fibre-cells, which, accord- 

 ing to my own opportunities of observation, are developed on the 

 same general plan, that is, by the formation of sarcous substance, 

 first, in the shape of fibres or lateral bands along the sides of a nucleus 

 more or less encrusted with blastema, so that the organic muscular- 

 fibre-cell would appear to represent an early stage in the development 

 of the striped muscular fibre. 



As incubation advances, the fibres acquire a tubular investment of 

 the contractile or sarcous substance, which gradually increases in 

 thickness or depth, and appears on each side as a band of corre- 

 sponding breadth. As they grow in length, they also contract in 

 diameter, and become of uniform structure throughout ; while their 

 nuclei rise nearer to the surface, and assume a more oval form. At 

 this period the marks of striation, either longitudinal or transverse, 

 are only faint and occasional, 



By the fourteenth day of incubation, the entire substance of the 

 fibres separates into longitudinal fibrillse, which in turn become shortly 

 resolved into particles or sarcous elements. After this the fibres 

 continue to grow in thickness by the addition, to their surfaces, of 

 new fibrillse, which, as usual, are formed around nuclei encrusted 

 with blastema cementing them, in such cases, to the original fibre. 



In mammalia, although there are some particular but unimportant 

 differences in the development of muscular fibre, the general plan is 

 the same as in birds. The nuclei at least in the ox, sheep, and 

 pig are larger, and have more distinct cell-walls or enveloping 

 membranes. The fibres of the sheep or pig first make their appear- 

 ance, in the foetus of from half to three-quarters of an inch in length, 

 as thick and nearly parallel threads lying amongst a densely crowded 



