STRIATED MUSCULAR FIBRE IN MAMMALIA. 
247 
rough and irregular, obviously from the addition of fresh material, Plate VII. fig. 5. 
Sometimes these bands appear defective or broken at intervals, or altogether wanting 
for some little distance. This no doubt is the result of the manipulation required for 
the microscope. 1 have occasionally seen fibres, which, either from the same cause 
or from some defect in their formation, possessed only one lateral band ; the extremi- 
ties of the nuclei being invested on one side only. 
If a portion of muscular tissue be examined which has been roughly dissected, or 
which has been taken from a foetus previously kept for a few hours in water, fibres 
will often be seen which are more or less broken up. Some will be found with the 
lateral bands separated from or partly stripped off the nuclei and variously twisted. 
The nuclei themselves will be wanting in many places, or considerably disturbed. 
These and other derangements, the result of violence, assist to explain the construc- 
tion of the fibres at this period of their development. 
It is interesting to compare the arrangement of the nuclei in this stage of deve- 
lopment of muscular fibre in Mammalia with the position of the nuclei in the fully- 
developed fibre of some of the lower classes. Mr. Bowman, in his paper in the Philo- 
sophical Transactions, has noticed that in the muscular fibre of many insects and 
of some reptiles, the corpuscles are disposed along the central axis of the fibre witii 
remarkable regularity, and in some instances, as in the Tipula (Harry Longlegs), 
which he figures, the corpuscles are thus arranged with their long axis transversely, 
(See fig. 6 a, and compare it with figs. 3 and 7, Plate X.) The central row of nuclei 
is well shown in the fibres of the leg of the common Blue Bottle Fly {Musca vomi- 
toria) after the addition of a weak acid. In insects, the nuclei are very often visible 
in the fibre without any previous preparation. I have sometimes distinctly observed 
them in fibres from the leg of the Tipula, and in many other examples. 
The fibres next increase in length and the nuclei separate ; the nuclei remain no 
longer in close contact ; small intervals appear between them, and as they have more 
space they increase in width and become more nearly circular. The spaces between 
the nuclei rapidly widen, until at last they lie at a very considerable distance apart. 
At the same time the fibre decreases very considerably in diameter, and the cause ot 
this is sufficiently obvious. As the nuclei part from each other and as the spaces 
between them increase, the bands which they separated fall in,— approach each other 
and ultimately coalesce*. This fact is placed beyond doubt by the examination of 
some fibres in which these changes are in progress, Plate X. fig. 8. At one extre- 
mity of a fibre may be seen the oval nuclei packed closely together, and bordered at 
their extremities by the substance of the fibre; further on they may be seen sepa- 
rating and becoming l ounder, the bands at the same time are beginning to approxi- 
* For example, in a specimen of muscular tissue from a foetal pig inches long three fibres were measured. 
In the first the nuclei were almost in contact, and the width of the fibre was y^Voth of an inch ; in the second 
the nuclei were apart, and the width of the fibre was -2^0^ ^ the third the nuclei were 
xA^th of an inch apart, and the width of the fibre was -5-xo-o • 
