116 Mr. W. M. Dobie on the Minute Structure 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). 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. | i 
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. 6 a). cara ae 
5. That it seems probable that there exists a homogeneous 
connecting medium among the fibrille (fig. 8a & 6). , 
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 fibrille, 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 mstrument, causing a pecu- 
liar appearance of movement on the fibrille (fig. 6 a & 8). 
9. That the clear spaces are generally narrower in the fish 
and lobster than in the frog and mammalia (fig. 6a). 
10. That the fibrillee 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 striz, 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 striz 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 arational manner, and I believe that Mr. Erasmus Wilson is 
