1897] MICROSCOPICAL JOURNAL. 75 



fibrils aud bear a similar relation to the tibres that the 

 i'asicles do to the muscle. 



Each fibre, moreover, contains nuclei. They are oval 

 bodies, the long axis usually placed paralled with the 

 longaxis of the fibre (Fig. 3). The position of nuclei varies 

 greatly in the difterent animal forms and for this reason 

 special stress is laid upon it in this discussion. The 

 points to be emphasized are, the position and number of 

 nuclei imbedded in the sarcous substance and the relative 

 sizes of the different fibres. The animals have been 

 chosen from widely varying classes to give a fair repre- 

 sentation of all types. They are taken up in order, ac- 

 cording to their classification in the animal kingdom. 



The fish representative is an elasmobranch, the dog- 

 fish. Its striped muscle fibre is long aud cylindrical as 

 is usual. At its ends it tapers suddenly, the striated 

 condition is lost and only the connective tissue covering 

 stretches out into muscle attachment. The fibres vary in 

 width but an average diameter of twenty fibres, as shown 

 in section, is 74 microns. The nuclei are imbedded in the 

 sar(^ous substance and only rarely is one found by the 

 edge, making but eleven per cent of the whole number in 

 this position. 



The frog is the amphibian representative (Fig. 4). 

 The different fibres vary greatly in width, those nearer 

 the outer edge of a muscle section appearing much 

 smaller. This may be due to the fact that the fibres ter- 

 minate on the outer edge in the sheath of muscle. The 

 average diameter of twenty fibres as shown in section is 

 66 microns. The only measurements found mentioned ar« 

 those given by Gage (Reference Handbook of Medical 

 Science, Yol. V. p ): the approximate width is 56 mi- 

 crons for amphibians. 87 per cent of the nuclei are im- 

 bedded in the sarcous substance. A transection of a 

 fibre shows from one to six nuclei. The frog is quite a 



