252 
MR. SAVORY ON THE DEVELOPMENT OF 
visible. Nuclei may be seen in all stages of their progress passing from without into 
the substance of the fibre, and hence the majority appear placed at or near the 
border of the fibre. Many granules are visible, scattered irregularly throughout 
the fibre, Plate XI. fig. 12. 
After birth the fibres enlarge with a considerably increased rapidity; they very 
soon attain a large size, and ere long reach the adult condition ; but for some time 
the variation in the diameter of different fibres is very obvious. In the pig, the striae 
(sarcous elements ?) attain their full size two or three weeks after birth. 
In the development of muscular fibre, then, the following stages may be traced : — 
Aggregation of cytoblasts, and their investment by surrounding blastema. 
Their regular arrangement into a single series. Formation of lateral bands. 
The lengthening of the fibre and separation of the nuclei. Approximation of 
bands. The appearance of striae. 
The further development of the fibre and its growth, by the addition of fresh sub- 
stance to its exterior, by means of the surrounding nuclei. 
Condensation of the fibre. 
Now it may have been understood from the foregoing description, that these several 
stages do not follow one another as a simple consecutive series. On the contrary, 
two of the above processes are generally proceeding at the same time. For instance, 
during the whole period of development, fresh material is being continually added to 
the fibre, at first independently, and afterwards by means of additional nuclei ; while 
the nuclei are rearranging themselves into a single row, fresh blastema is constantly 
added to that which already invests them. The bands bordering the nuclei are con- 
tinually increasing by the addition of fresh material ; so that, as previously explained, 
the longer the separation of the nuclei is delayed, the thicker do they become ; and 
in those fibres especially in which many of the nuclei perish before they have sepa- 
rated, the lateral bands attain a very great breadth, and the fibres a very considerable 
diameter. 
So also, as already stated, the fibres at a subsequent period continue for some time 
to decrease in diameter, although fresh material is being added by means of addi- 
tional nuclei. 
As a general rule, all fresh material which is added to the fibre before the original 
nuclei separate, is attracted independently of fresh nuclei, but that which is added 
after the original nuclei have separated or become disintegrated, is by means of the 
additional nuclei which are attached to the exterior of the fibre. The exceptions 
occur in those fibres in which the lengthening appears delayed much beyond the 
usual time, and until after the majority of the original nuclei have disappeared. (See 
Plate XI. fig. 13.) In these cases nuclei in great abundance are often seen attached 
to the surface of the fibre. They are frequently so abundant as to be absolutely in 
