1087 



it WMS tested hv Sanderson and (.toTscii" in tlic case 

 of the TliDriihaek (lUijd cJnrala) and found 1o !n' aliout 

 '/,„ of that possessed l)y tlie electric orf^'ans of tiie 

 Tori)e(h). Sn-iinge to say, however, thcise so-called 

 pseudoeleetric orgaiis of our eonnnon Kays are situated 

 in an entirely different part of tiie body from the elec- 

 tric organs of the ToypcdiuUhe. \\'iiercas the latter 

 (fig. 30.j, 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 dift'erenee 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 



Fig. 305, An Electric Hay (Toi-jjkIo iiiarmorala) wiih tlic skin re- 

 moved from tlie electric organs (iJ), the skull (S), and the biancliinl 

 cavities (A'). 0, eyes; Sp, spiracles. After Wiedehsueim. 



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, (dose 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 orgaTis ])elong and the innerva- 

 tion of the organs. Such a genetic connexion Ijetwcen 

 these organs in the diffei'cnt fishes as that one form of 

 them can have derixcd its origin immediately from the 

 otiier, 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 

 Babuciiin'' in the case of the Rays, and was still more 

 clearly elucidated by Fhitsch's examination' of the 

 Electric Eels brought home by Sachs; but a special 

 interest, of a yet wider inqjortance, attaches to Ewart's 

 investigations' of the de\elopment of the electric ele- 

 ments in our eonnnon Kays. From these researches it 

 appears as if we might be able to deduce from the 

 structure of the electric organs an exj)lanation of the 

 composition of striated muscular tissue and of the im- 

 portance of the different substances in this composition'. 

 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 fron^ other embryonic cells. 

 In a common Ray, on the other hand, that part of the 

 upi)er caudal muscles which is destined for conversion 

 into a pseudoeleetric 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 sarcopJasma probably to intercept and 

 store the electricity, the rhabdia to serve as a non-con- 

 ductor. In the common Skate (Boja hatis), 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. (7' . cm.) and has its entire organic sys- 

 tem, even the muscles, typically formed. In the Starry 

 Ray {Ihija radkita) the development of the electric 

 orirans does not commence until the fish measures 12 



" JouYn. Physiol., vol. 9, Xos. 2 and 3. 



' Centralbl. Medicin. Wiss. 1870, p. 259; Arch. Anat., Physiol. 187G, p. 501. 



' Dr Carl Sachs Vnters. am Zitteraal, Leipzig 1881. 



'' Phil. Trans. Eoy. Soc. Lontl., vol. 179 (1888), 13, pp. 399 and 539. 



' Cf. above, p. 662, on Rollett's investigations of (he muscle fibres in Hippocampus. 



