80 



ELECTRO-PHYSIOLOGY 



CHAP. 



FIG. 19. Transverse section of two float-muscles of Hippo- 

 campus. (Ms), Bundles of fibrils (muscle -columns); 

 (Sp), sarcoplasm. (Rollett.) 



muscles of the same animal ; and the same is true of the 

 position of the nucleus. Two groups of striated fibres can again 

 be distinguished in vertebrates, i.e. those which have much, and 

 those which have little, sarcoplasm. The fibres of the first group, 

 generally, look rather dark when examined with the microscope, 



owing to the large num- 

 ber of interstitial " gran- 

 ules " with which the 

 Sp sarcoplasm is studded ; 

 the cross -striae are in- 

 distinct, the longitudinal 

 well marked. The a- 

 plasmic fibres, on the 

 other hand, are clearer 

 and transparent, with 

 sharp transverse striae. 

 In the same sense, we 



have already, in describing the structure of the uni- 

 nuclear muscle -cells of invertebrates and vertebrates, had 

 occasion to distinguish between clear and dark, plasmic and 

 a-plasmic elements; cardiac muscle -cells in particular being 

 universally dark and plasmic. The float muscles of the Sea- 

 horse (Hippocampus) exhibit 

 a peculiarly typical example 

 of plasmic, multinuclear 

 muscle-fibres in the Verte- 

 brates. In transverse sec- 

 tion the flat bands of muscle- 

 fibrils (muscle-columns) are 

 seen, as in the muscles of 

 Salpa, or the cardiac muscle 

 of Crustacea (supra), form- 



Fio. 20. Transverse section of lateral muscle-fibres 

 of Carp. (Kolliker.) 



Sp -- 



-Ms 



ing irregular groups and 

 columns in the sarcoplasm, 

 which is here excessively abundant, and presents a thick 

 cortical layer in which the nuclei are embedded (Fig. 19). 

 Similar bands of muscle-columns are found in the lateral muscles 

 of the carp, which are also characterised by an abundance of 

 nucleated sarcoplasm lying close under the sarcolemma (Fig. 20). 

 Other muscle-fibres (lateral trunk-muscles) in the same fish 



