74 Proceedings of the Royal Physical Society. 
and that in the latter a shifting of the nerve supply took 
place, it is also quite certain that no fish could possibly 
have all, or even the larger part, of its muscles transformed 
into electric organs, for the animal would at least be required 
to feed itself, and so move its jaws, and have some power of 
locomotion. These movements would of necessity insure some 
of its fibres remaining permanently as muscles. 
We have thus, in the development-history of the electric 
organ—(1) an indifferent stage, ze, a stage in which the 
fibres of future muscle and future electric organ are exactly 
alike; this stage, however, is of short duration, for it is 
(2) very quickly followed by one extremity of the fibres 
becoming club- or mace-shaped in those fibres which are 
destined to form the electric organ. This club-shaped condi- 
tion may be permanent, as in &. radiata, or (3) may advance 
further and become either cup-shaped, as in aia cirewlaris 
and &. fullonica, or (4) may become flattened out to form 
the complicated discs of &. batis and &. clavata, or (5) may 
be still further modified to form the simple hexagonal plates 
of the Torpedo or Electric Ray. 
It is a noteworthy fact that electric organs occur only in 
the fish group, and are practically confined to two sub- 
divisions of this group, viz., Elasmobranchs and Teleosteans ; 
also that in these fishes they do not occupy the same position 
in all genera, for whilst in the Skate section they occupy the 
tail region, in the closely related Torpedo they are in the 
head region—one organ on each side of the jaw, between the 
dorsal and ventral surfaces. This of course seems to show that 
the electric organs of the Skate and Torpedo have not been 
inherited from a common ancestor. Probably the electric 
organ of the Skate has been later in forming, as, according to 
Professor Ewart, it is still on its way to further development; 
and yet, if my theory be a correct one, the electric organ 
must have commenced developing before the motor plate— 
or rather its equivalent (the various nerve branchings)—had 
shifted its position to the centre of the muscle fibre, or at all 
events before the motor plate had lost its connection with 
the anterior extremity of the muscle fibre. It1is almost certain 
that the motor plate of muscle fibre, and the nerve endings 
