482 
MR. BOWMAN ON THE MINUTE STRUCTURE AND 
inactivity at other periods of life, and no difference has appeared to occur in it, 
whether the specimens examined were flaccid or firm, pale or dark-coloured. In 
Birds, an exceedingly delicate sarcolemma may be occasionally seen connecting the 
broken ends of a fasciculus, but it is rare to discern any contraction under the 
microscope in fasciculi inspected even instantly after death, so quickly does their irri- 
tability cease ; and where vesicles are discovered, they are small and transparent, 
and would be apt to pass unnoticed unless specially sought for. What may be con- 
nected with this circumstance is, that the fibrillse show a great proneness to fail 
asunder in this class, their adhesion to one another being but slight; the transverse 
strise are often much deranged by dark irregular longitudinal streaks, and in a trans- 
verse section, as already seen, the fibrillse are shown more isolated and distinct than 
in any other examples. In Insects, I have repeatedly seen the sarcolemma raised from 
the surface of the fibrillse, where they were undergoing contraction (figs. 71 to 74.). 
With regard to the use which this remarkable structure may be intended to serve 
in the economy of the organ, our present ignorance of the essential cause of motion 
renders any explanation that might be offered, of doubtful value. But it has appeared 
probable to me, 1st, That it may act as a mechanical protector and isolator of the 
contractile tissue inclosed within it ; 2ndly, That its exquisitely smooth external 
surface may facilitate those rapid minute motions of neighbouring fasciculi one 
against another, which will afterwards be shown to occur, in all likelihood, in con- 
tracting muscle; and Srdly, That, from its apparent similarity in structure to the 
membrane of the nervous tubules, which run among the fasciculi, and between 
which and the proper contractile tissue it seems certainly to intervene, as well as 
from its extensive contact and union with the surface of the latter, it may be the 
conducting medium of that influence, whose mode of propagation the late discoveries 
of the loop-like termination of the nerves of muscle, have hitherto only seemed to 
render more inexplicable than ever. 
Of the Corpuscles of the Primitive Fasciculi. 
There is a fact in the anatomical history of voluntary muscle which, from its appa- 
rent universality, is entitled to some attention, and yet which seems hitherto to have 
escaped the notice of anatomists ; this is, The existence in the primitive fasciculi of 
minute bodies of a definite form and structure, generally invisible, unless rendered 
evident by special modes of preparation. The most ready method of demonstrating 
them, is to touch the specimen with a small quantity of one of the milder acids, as 
the citric. These agents cause an instantaneous tumescence and transparency of the 
fasciculi, as has already been stated, and the corpuscles become at once clearly de- 
fined. But by the swelling of the fibrillse among which they are situated, they may 
be seen to undergo some distortion from their real shape, and it is generally in certain 
parts alone, as where fibrillse have escaped from the sarcolemma, or the corpuscles 
become detached, that they present their natural characters. They then appear to be 
