KAYS. 
1087 
it was tested by Sanderson and Gotsch® in the case 
of the Thornback ( Baja clavata ) and found to be about 
7 10 of that possessed by the electric organs of the 
Torpedo. Strange to say, however, these so-called 
pseudoelectric organs of our common Rays are situated 
in an entirely different part of the body from the elec- 
tric organs of the Torpedinidce. Whereas the latter 
(fig. 305 , E ) lie on the sides of the head and the 
branchial cavities, the former are placed on each side 
of the dorsal line of the tail. With this difference are 
connected two other essential dissimilarities: the nerves 
which run to these organs are of a totally different 
origin in the Electric Rays and the common Rays, and 
the arrangement of the respective organs is entirely un- 
like. The electric organs of the Torpedinoids lie in 
0 
Fig. 305. An Electric Ray ( Torpedo marmorata) with the skin re- 
moved from the electric organs ( E ), the skull (S), and the branchial 
cavities ( K ). 0 , eyes; Sp, spiracles. After Wiedeksheim. 
the region of the transverse muscles, the levators and 
depressors of the branchial arches, and are supplied 
with nerves from the fifth and tenth cranial pairs and 
have their elements transversely arranged — the piles 
are vertical. The electric organs of our common Rays, 
on the other hand, are situated in the region of the 
great caudo-lateral muscles, at the lateral edges of the 
tail, close under the skin, and their nerves are spinal, 
their elements arranged in the longitudinal direction of 
the body. The difference thus affects both the parts of 
the body to which the organs belong and the innerva- 
tion of the organs. ■ Such a genetic connexion between 
these organs in the different fishes as that one form of 
them can have derived its origin immediately from the 
other, we can therefore scarcely expect to find; but 
they have one thing in common, their development 
from muscular substance: — the electric organs are 
transformed muscle fibres. This was first shown by 
Babuchin'' in the case of the Rays, and was still more 
clearly elucidated by Fritsch’s examination c of the 
Electric Eels brought home by Sachs; but a special 
interest, of a yet wider importance, attaches to Ewart’s 
investigation s'* of the development of the electric ele- 
ments in our common Rays. From these researches it 
appears as if we might be able to deduce from the 
structure of the electric organs an explanation of the 
composition of striated muscular tissue and of the im- 
portance of the different substances in this composition e . 
A muscle or a portion thereof may be converted 
into an electric organ at entirely different periods in 
the life of the fish. In the Torpedo, for instance, this 
transformation takes place at an early stage, during its 
embryonic existence within the egg and almost simul- 
taneously with the appearance of muscular cells, before 
these are fully differentiated from other embryonic cells. 
In a common Ray, on the other hand, that part of the 
upper caudal muscles which is destined for conversion 
into a pseudoelectric organ exhibits the same for- 
mation in the larval stage as the other parts of these 
muscles, with the typical composition of the muscular 
fibres unaltered; and the observation of the subsequent 
changes shows in a series of different developmental 
stages how one constituent of the muscle fibre sepa- 
rates from the other, each being destined for a distinct 
purpose, the sarcoplasma probably to intercept and 
store the electricity, the rhabdia to serve as a non-con- 
ductor. In the common Skate {Baja batis ), for example, 
this indeed takes place before the embryo leaves the 
egg-capsule, but not until it has attained a length of 
about 3 in. (77 2 cm.) and has its entire organic sys- 
tem, even the muscles, typically formed. In the Starry 
Ray {Baja radiata ) the development of the electric 
organs does not commence until the fish measures 12 
“ Journ. Physiol., vol. 9, Nos. 2 and 3. 
b Centralbl. Medicin. Wiss. 1870, p. 259; Arch. Anat., Physiol. 1876, p. 501. 
c Dr Carl Sachs Unters. am Zitteraal, Leipzig 1881. 
d Phil. Trans. Roy. Soc. Lond., vol. 179 (1888), B, pp. 399 and 539. 
e Cf. above, p. 662, on Rollett’s investigations of the muscle fibres in Hippocampus. 
Scandinavian Fishes. 
137 
