xr ELECTRICAL FISHES 389 



(isotropous) lamelke become " optically more homogeneous, more 

 strongly refracting on the whole, and therefore firmer (less watery)," 

 while on the other the metabolous strata (particularly those 

 of the transverse discs) lose in refractability, which simultaneously 

 diminishes their power of double refraction. The amount of this 

 diminution is, however, " nil in contraction, as compared with that 

 in the transformation of muscle-fibres into the meandering layer of 

 the electrical compartments." It is, moreover, apparent at such an 

 early stage of development (previous to the club-shaped swelling 

 of the proximal end of the muscle-fibre) that no other sign of 

 approaching transformation can yet be detected. At this point, 

 again, the phylogenetically younger status of the organs of Raja 

 radiata is apparent, since the double refractility here dis- 

 appears much more slowly and incompletely than in other kinds 

 of the same species (R. ~batis, clavata, circularis). This reaction 

 during the transformation into electrical organs gives substantial 

 confirmation to Engelmann's conjecture that " only the doubly- 

 refracting metabolous elements of the muscle-fibrils are the seat 

 and source of the contractility of the muscle." 



The development of the " pseudo-electric " organ in Mormyrus 

 is much less certain than that of Raja. Yet here, too, Babuchin 

 (1) was able, on investigating six varieties of the species, to state 

 definitely that " the electrical organs are again developed from 

 muscles, and retain their muscular characteristics even when the 

 formation is perfect." Each " plate '" of Mormyrus consists of 

 three laminae that can be separated from one another, the two 

 outer being " structureless, invested from the inner side with a 

 layer of granulated substance, and set with numerous rounded 

 nuclei." One of these laminae is the immediate prolongation of 

 the sheath of the pale (ingoing) nerve-fibres. The middle layer 

 consists exclusively of very thin flattened muscle-fibres or bands, 

 lying irregularly near each other. Each single fibre is sharply 

 striated, while collectively they form a muscular lamina of 

 firmer consistency towards the border of the electrical plate than 

 in the centre, with no meandering markings. According to 

 Babuchin, therefore, the electrical plate of Mormyrus does not 

 correspond outogenetically with a single metamorphosed nerve- 

 fibre, as in Torpedo or Raja, but with " an entire bundle of short 

 muscle-fibres, as found in the lateral trunk-muscles of fishes." 



Fritsch (12), too, affirms that a tissue of varying density is 



