LISTER, ON INVOLUNTARY MUSCULAR FIBRE. 5 
rounded particles, beautifully distinct (fig. 12). Deeper in the 
organ were similar cells, smaller in size and imperfectly de- 
veloped, evidently destined to supply the place of those ripe 
for expulsion. The connecting tissue between and among 
these ova displayed many of the ordinary parenchymatous 
cellules within its substance. 
To facilitate identification, I subjoin in conclusion a few 
particulars gathered from Professor Forbes’s monograph, in 
which Thaumantias inconspicua, T. punctata, and T. Thomsoni 
differ from this species. The first has the dise wider and 
more flattened, also, purplish-coloured glands and twenty ten- 
tacles. The second has thirty-two tentacula, is a larger 
species, with the umbrella more depressed. The third has 
but sixteen tentacula, the bulbs and reproductive glands con- 
taming a yellow pigment. There is no other British species 
for which it can be readily mistaken. The great length of 
the tentacula forms a distinctive peculiarity. I have desig- 
nated this Medusa, Thaumantias achroa (&xpoos, colourless). 
On the Minute Srructure of Invotuntrary Muscutar 
Fisre. By Josepn Lister, Esq., F.R.C.S. Eng. and 
Edin., Assistant-Surgeon to the Royal Infirmary, Edin- 
burgh. Communicated by Dr. Curistison. 
(From the ‘Transactions of the Royal Society of Edinburgh” Read 
December ist, 1856.) 
Ir has been long known that contractile tissue presents 
itself in the human body in two forms, one composed of fibres 
of considerable magnitude, and therefore readily visible under 
a low magnifying power, and marked very characteristically 
with transverse lines at short intervals, the other consisting 
of fibres much more minute, of exceedingly soft and delicate 
aspect, and destitute of transverse striae. The former variety 
constitutes the muscles of the limbs, and of all parts whose 
movements are under the dominion of the will; while the 
latter forms the contractile element of organs, such as the 
itestines, which are placed beyond the control of volition. 
There are, however, some exceptions to this general rule, the 
B § 
