116 Mr. W. M. Dobie on the Minute Sti-udure and 



c. That the edges of the clear space can be seen under a fine 

 instrument not to extend farther laterally than the edges of the 

 dark space (fig. 6 a). 



[I perceive Mr. Quekett in one of the plates to his recent 

 work on the Microscope has distinctly represented this, though 

 he gives an incorrect diagram to explain an appearance which he 

 represents quite correctly.] 



d. That the cross-line in the clear space measures exactly the 

 same as the breadth of the dark space, and that it can be di- 

 stinctly seen in favourable cases to touch the edges of the clear 

 space (fig. Qa). 



5. That it seems probable that there exists a homogeneous 

 connecting medium among the fibrillse (fig. 8 a & ^). 



6. That the structure of cross- striated muscular fibre is essen- 

 tially the same in all the members of the animal kingdom. 



7. That from all I have seen of the structure of voluntary 

 muscle, I am perfectly certain that the appearances presented are 

 quite inconsistent with any palpable spiral arrangement, either 

 in the fibre or fibrillse, as is still the opinion of Dr. Martin Barry. 

 Mr. Bowman^s observations ought to have set this point at rest. 



8. That the dark spaces become clear, and clear spaces dark, 

 during a change in the focus of the instrument, causing a pecu- 

 liar appearance of movement on the fibrillse (fig. Q ahb). 



9. That the clear spaces are generally narrower in the fish 

 and lobster than in the frog and mammalia (fig. 6«). 



10. That the fibrillse are somewhat flattened bands. 



11. That the dark spaces in some cases appear as if slightly 

 elevated above the clear spaces of a fibril (fig. 7 a). 



The transverse striae. 



The transverse striae, when observed with great care and during 

 rapid though slight alterations of the focus, are seen to undergo 

 some change in appearance; a kind of shifting a short space 

 backwards and forwards. This appearance I explain in the fol- 

 lowing manner. 



The muscular fibrils being composed of a series of clear and 

 dark particles, which under change of focus alter from dark to 

 clear and from clear to dark, this change also takes place under ^ 

 the same circumstances in the complete fibre, so that the dark 

 transverse striae are at one time formed by the lateral coaptation 

 of the dark spaces, at another time by a like coaptation of the 

 clear spaces. 



I see no other way of explaining this peculiar appearance of 

 movement on the surface of the fibre during alterations of focus 

 in a rational manner, and I believe that Mr. Erasmus Wilson is 



