544 H- ^- BERNARD, On the Relation of the isotrop, to the anisotrop. Layers. 



Fig. 4. Peculiar staining of a muscle, the fibrils of which showed 

 no striation ; for suggested interpretation see text p. 540. 



Figs. 5, 6, 7, 8. Fully (? abnormally) expanded elements. Fig. 5 shows 

 the zig-zag arrangement generally found under these conditions. 



Fig. 9. Fibril from Fig. 1 showing in its length various stages 

 of the "element" from full expansion to contraction. 



Figs. 10, 11, 12, 13. Fibrils showing the assumed normal degree 

 of expansion. Fig. 13 was near the very end of the fibril where the 

 length of the "elements" is often irregular, cf. Fig. 23. 



Fig. 14. Fibril from Fig. 2, showing different phases of the "elements". 



Figs. 15 and 16. Fibrils entering upon the homogeneous stage. 



Fig. 17. Fibrils in the homogeneous stage. 



Fig. 18. Homogeneous stage passing into the contracted or inverse 

 stage. 



Figs. 19, 20. Fully contracted fibrils ; the inverse stage. 



Figs. 21 and 22. The same; 22 is intended to show the highly 

 refractive swollen ends of the "elements". 



Fig. 23. (cf. Fig. 13) to show the end of a fibril having the ter- 

 minal "elements" longer than the rest. 



Fig. 24. Diagram founded upon the foregoing, the measurements 

 being taken from Engelmann's tables (p. 538). A expanded, S homo- 

 geneous, C inverse or contracted stage. K Krause's discs. * isostropous 

 layers, i' and i" Engelmann's persistent isotropous layers seen under 

 polarised light (cf. however text p. 535). a anisotropous layer, a" the 

 length of Engelmann's anisotropous layer in the contracted fibril. The 

 shortening of a to a" is seen to be unable to account for the whole 

 contraction of the element, m Hensen's discs, considerably widened in C. 



Fig. 25. A wing muscles of Musca vomitoria untired. B the 

 same, exhausted, both drawn to scale. In A these elements have 

 their typical form and striation, and were 2 /.i in thickness, the sarco- 

 somes being 1 ^. In ^ the striation has disappeared, the fibrils measured 

 slightly less, and the sarcosomes slightly more than 2 j^i across. 



Figs. 26 and 27. Two stained muscle fibres of Galeodes, showing 

 different arrangements of staining substance. 



Fig. 28. The same in cross section, the extremely delicate sarco- 

 lemma is not drawn : the nuclei have not stained. 



Fig. 29. Ditto, the stained nuclei are seen in a row in the axial 

 sarcoplasm, the fibrils remaining unstained. 



Fig. 30. Wing muscle, showing in addition to Krause's discs the 

 dark bands in the middle of Hensen's clear spaces. 



Fig. 31. Diagram showing the probable origin of both these dark 

 bands, as the optical expression of strains as indicated by the arrows. 



