Note on Muscle Fibre, Electric Disc, and Motor Plate. 73 
words, at right angles to the direction in which it enters the 
disc, cup, or plate. 
It was therefore with no little surprise that I observed, 
on carefully examining the isolated muscle fibres of an adult 
skate (probably &. batis, but unfortunately I did not make a 
note of the species at the time), that one extremity was 
slightly larger than the other, and that this larger end was, 
further, hollowed out or excavated to a slight extent. It is to 
this hollowing out that I especially wish to call attention. 
What does it indicate? Is it a mere accidental condition, or 
does it point to a time when the muscle fibre, like the electric 
disc or cup, received its nerve supply at its anterior end ? 
To me this latter alternative seems to be the right explana- 
tion, viz., that the concavity at the end of the striped muscle 
fibre does indicate the primitive position of the motor plate. 
To account, therefore, for the present position of the motor 
plate, we have two alternative explanations, viz., (1) that the 
original anterior motor plate, or its equivalent (nerves to disc), 
has disappeared, and that the lateral or true motor plate of 
muscle fibre is a secondary formation ; or (2) that the motor 
plate is really the original one (or its equivalent), which has 
gradually (in the course of ages) shifted its position till it 
now comes to occupy one side of the muscle fibre, somewhere 
about the middle of its length. 
It would appear that a motor plate situated about the 
centre of the fibre is more advantageously situated for 
purposes of quick contraction of the fibre than one situated 
at its extremity. Be this as it may, it is certain that all motor 
plates are situated about the centre of their respective fibres. 
One can imagine that, given all muscle fibres provided 
with nerve supplies at one of their extremities, and that 
under certain conditions, of which we are still wholly 
ignorant, some of the fibres developed into electric discs, 
which collectively constitute the electric organ, whilst 
others collectively went to form various groups of muscles,’ 
1 It is to be regretted that no terms have been coined, so far as I am aware, 
to distinguish between fibres which remain as muscle fibres and those which 
transform themselves later on into electric discs, cups, or plates, Such terms 
would be very convenient. 
