472 
MR. BOWMAN ON THE MINUTE STRUCTURE AND 
is evidence of an interesting kind that the fibrillee are beaded, and the striae formed 
in the manner here above contended for. The light and dark points of the fibrillee 
are capable of being reversed by varying the focus, which shows that they are an 
appearance occasioned by refraction, the phenomena being precisely those presented 
by the beaded vibrio, which they often nearly resemble in form as well as size. On 
the whole, little doubt remains on my mind that the fibrillee consist of a succession 
of solid segments or beads, connected by intervals generally narrower, and I believe 
the beads to be the light, the intervals the dark spaces, when the fibril is in exact 
focus. Considerable variety is to be met with in the relative size of these two parts, 
but generally they are nearly alike. When there is a difference, it is commonly in 
favour of the light. In the accompanying sketches of various specimens of fibrillee, 
it will be seen that the segments are by no means all of one form. In the new-born 
Rabbit they present the oval figure, the long diameter of each being in some exam- 
ples parallel to the fibrillee, in others oblique. The striae formed by these last are also 
seen (fig. 10.). In the Chameleon the same thing is observed (fig. 14.). In the ocular 
muscle of a fish, there is an appearance of the beads overlapping, and of a lozenge 
shape (fig. 1 1.). In the heart of the Turtle the long diameter of the beads is across 
the fibrillee (fig. 12.). The psoas muscle of the Hare presented several fibrillee, in 
which the beads were further apart than usual, and of an oval form. In one state of 
the focus they were altogether light, and the intervals wholly dark ; but in another, 
the beads were surrounded by a thick circumference of shadow, and a light streak 
appeared in the centre of the dark interval (fig. 15.), an appearance precisely similar 
to that which I have observed to take place in beaded rods of glass with elongated 
intervals*. In endeavouring to carry my investigations further into the intimate 
structure of these fibrillee, I have hitherto been completely baffled ; nor does the sub- 
ject encourage very sanguine hopes as to the event of such a search, at least without 
higher powers of the microscope than we at present possess. From the sections, how- 
ever, already described, and especially those of the fasciculi of Birds, the fibrillee 
seem plainly to possess a circular transverse outline. 
From such varieties in the fibriilse, it is not wonderful that corresponding ones in 
the striae should result, and some of the most remarkable met with since the com- 
* It is not intended to be implied that the above varieties are peculiar to the several animals from which 
they are taken, or that in these animals similar appearances will uniformly be met with. On this subject 
(that of form), a much more extended inquiry is requisite, and I would again express my dissatisfaction with the 
above observations, as being made on detached, and therefore mutilated, parts. Indeed it may be doubted, 
whether, in the agglomerated state of the segments, their outline do definitely exist on all their aspects ; and 
whether it be not rather essentially incomplete, through their adhesion to one another. If, however, as ap- 
pears evident from their refractive powers, the segments are more solid than the medium which connects them, 
and if they are rounded, and not rectangular, in form, which, after examination with the best instruments, is 
still confessedly uncertain, interstices must exist, capable, perhaps, of facilitating the motions occurring between 
these parts. 
