36 ELECTRO-PHYSIOLOGY 



superposed nets of filaments, consisting of the cell processes of 

 the muscle-corpuscles, and only connected longitudinally by fine, 

 small fibres. Apart, however, from the fact that the appearance 

 of a muscle-fibre in optical transverse section must then vary 

 with alterations of the objective, according as the cross-section of a 

 fibre-plexus, or the space between two such, is focussed (when in the 

 first case Cohnheim's area?, in the second a mere system of dots, 

 corresponding with the cross-sections of the connecting longitudinal 

 fibres, would appear which never is the case), the comparative 

 study of the development and structure of fully developed muscle- 

 fibres and cells of different animals appears to us to be conclusive 

 evidence against this theory. For the rest, it is sufficient to 



quote the masterly criticisms 

 of Eollett (20). 



The muscles of Flies ex- 

 hibit very peculiar structural 

 relations (Fig. 26). In trans- 

 verse section the bundles of 

 fibrils are once more flat and 

 band-like, and usually consist 

 of a single layer of fibrils 

 only. These, however, are so 



FIG. 2(5. Transverse section of striated muscle-fibres disposed ill SClieS that tWO 



of Musca domestica. A, Low power ; B, highly thrPP tnhp< flrp 



magnified; Ms, bands of muscle - columns Or 



(bundles of fibrils) ; Sp, sarcoplasm. (Schieffer- formed, fitting illtO 0116 



another, and separated by 



strata of protoplasm, with which they are also filled and sur- 

 rounded. The nuclei lie in the innermost, axial, plasma cylinder, 

 as appears in the longitudinal section of such a fibre. These few 

 examples will give an approximate idea of the multiplicity of 

 figures in cross -section in the " typical " arthropod muscles. 

 Before we pass on to the structure of the " a-typical " wing- 

 muscles (thoracic fibrils) of insects, the question as to the com- 

 position of " muscle-columns " out of " fibrils " must detain us for 

 a few moments. In Insect as in Vertebrate muscles, the direct 

 proof is harder to find than in many muscles of the Invertebrates. 

 Even under the most favourable conditions, e.g. after treatment 

 with gold chloride, which stains the sarcoplasm deep red or black, 

 while the fibrillar substance remains uncoloured, so that each area 

 of Cohnheim stands out distinctly, no further differentiation is 



