114 Mr. W, M. Dobie on the Minute Structure and 



this arises from the extremely small size of this space, especially 

 when the fibril is iu a relaxed condition, and is more particularly 

 found in the examination of the muscular fibrils offish, lobster or 

 crab, in which indeed this line can be very rarely seen (fig. 7 b). 

 Hence most probably the reason why ]Mr. Bowman does not re- 

 present it. In such cases the only way to obtain a view of it is 

 by stretching the fibril when in a perfectly fresh state; this 

 cross-line of the clear space in the lobster partook more of the 

 nature of a band, in the cases where I was enabled to examine it 

 (PI. VII. fig. 7 a). In the fish (salmon) I have only seen it in a 

 few cases, but in these the appearance was so distinct as not to 

 leave the least doubt of its existence. 



I am not aware that this cross-line in the lobster, salmon, skate 

 and frog has been seen by any preceding observers. In the pig 

 and human subject it has been seen ; I have also distinctly ob- 

 served it in the muscular fibrillse of the ox. 



The length of the dark and clear spaces is sometimes identical ; 

 at other times, and more frequently, the clear space is shorter ; 

 and in the lobster and salmon is often so narrow as to be dimi- 

 nished to a somewhat dark line when the fibril is in a perfectly 

 relaxed condition. 



I have also frequently observed, in dissections of the muscular 

 fibrillse of the frog and salmon, an appearance which I consider it 

 important to mention, the true explanation of which I am at pre- 

 sent unable to decide upon. It is as follows : — At the point where 

 two fibrillfe are separated from each other, extended for a greater 

 or less distance between them, there often exists a beautiful ho- 

 mogeneous membrane, (resembling the web between two of the 

 toes of a duck,) which is stretched by the violence used in the 

 separation of the fibrillse (fig. 8 a). In some recent observations 

 which I have made on the nmscular fibres of the skate when 

 perfectly fresh, this appearance invariably presented itself, with 

 this pecu.liarity however, that instead of being perfectly homoge- 

 neous, it was marked with stripes corresponding to the dark 

 and light spaces of the fibrillse between which it was stretched 

 (fig. 8 6). 



I was at first inclined to regard this membrane as a shred of 

 the sarcolemma accidentally stretched out between two fibrillse ; 

 but from its being of a decidedly more delicate nature than that 

 membrane, and from its being present in nearly every part of 

 some preparations, I am inclined to consider it as being caused 

 by some homogeneous connecting medium spread among the 

 fibrillse. 



The strise in this membrane in the skate I am at a loss to ac- 

 count for ; perhaps from the tearing of the membrane over the 



