Mode of Contraction of Voluntary Muscular Fibre. 117 
wrong in stating that the dark transverse striz are always formed 
by the lateral union of the /aght spaces. 
This appearance of movement cannot be caused by dark spaces 
of fibrille lying immediately below the clear spaces of a set of 
fibres which are superficial to them. As the movement can be 
seen in a perfectly fresh and undisturbed fibre, it can also be 
seen on the individual fibrille, as I have already stated. 
The contraction of voluntary muscle. 
Hales, Prevost and Dumas, from observations made on the ab- 
‘dominal muscles of the frog, considered the contraction of mus- 
cle to be due to zigzag flexures taking place in each fibre. Pre- 
vost and Dumas imagined it to be an electrical effect of the pass- 
age of nervous cords across the fibre at the angles of flexure. 
Professor Allen Thomson repeated the experiments of Hales, 
Prevost and Dumas, and was led from the observations he then 
made to consider that the zigzag plicee were not produced until 
the contraction had ceased in the fibres which were the subjects 
_ of it; he observed single fibres continuing in contraction, being 
_ simply shortened and not falling into the zigzag flexures. Pro- 
fessor Owen was also led to doubt the accuracy of the statements 
of Prevost and Dumas from noticing that during the contraction 
of unstriated muscles in some Filarias and in a Vesicularia, a 
swelling took place in the centre of the fibre which thus became 
shorter and thicker. 
Dr. A. Farre observed a similar fact in the unstriated muscles 
_ of the Polypifera. 
The admirable researches of Mr. Bowman have left us little to 
wish for with regard to the nature of the contraction ; I refer to 
his observations published in the ‘ Philosophical Transactions’ 
for 1842. All his observations were made on muscular fibres of 
animals shortly after death. 
I shall briefly allude to some observations made with reference 
to this subject on the living and uninjured tadpole. 
_ In April this year (1848), when observing the circulation in 
_ the tail of a tadpole after the disappearance of the gills, I was 
_ surprised on noticing that the cross-striated muscular fibres were 
distinctly visible through the external tegument; the contrac- 
tions after the animal was somewhat exhausted were slow and 
beautiful, not uniform throughout, as is the case when the tail is 
observed immediately after the death of the animal and stripped 
of its integument: the former is the active, living and voluntary, 
the latter the passive contraction. 
When the contraction was comparatively slow, the approach of 
the transverse striz could be seen with extreme distinctness ; the 
