MUSCLE. 135 



are also elongated in 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 lie 

 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 in 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 pi. IV, fig. 1, b, 

 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 



