380 ELECTRO-PHYSIOLOGY CHAP. 



discoid structure of which at once betrays it as an electrical organ 

 (Fritsch). It is more difficult to prove the muscular origin of 

 the electrical organ in the Torpedinidce and in Gymnotus. The 

 evidence must be sought in the developmental history, and in 

 comparative anatomy. 



Torpedo is peculiarly adapted for the study of ontogenetical 

 development. "This viviparous fish bears its young within itself 

 to an advanced stage of growth, so that the newly-born fishes are 

 already 6-8 cm. long, and able to give distinct electric shocks " 

 (Fritsch). 



The best observations in this department of anatomy, with its 

 important physiological bearings, are those of Babuchin (1), and 

 more recently Fritsch (12) ; de Sanctis having previously given an 

 erroneous description of the development of Torpedo. Ewart 

 (10) and Engelmann (8) have contributed further data of import- 

 ance to the " pseudo-electrical " organ of Raja. 



With regard to the development of the external form of the 

 body in Torpedo, de Sanctis distinguishes three main stages, 

 squaliform, rayiform, and torpediniform. At the end of the 

 first stage the position of the electrical organ can already be 

 recognised externally ; swellings which soon fuse together- 

 make their appearance upon the visceral arches at the point where 

 these bend to the ventral side. As soon as the trunk widens, 

 the embryo assumes the form of the common ray (stadium rayi- 

 forme), and the continuous forward progression of the discs at 

 last completes the characteristic rounded form of the electrical 

 ray. At this stage the electrical organ of the then developed, 

 but still unborn, fishes exhibits under the lens a delicate 

 punctuation the indications of the already perfected column 

 (Fritsch). 



At a very early stage in the development of the gill-arches, 

 as described above, these appear to consist of bundles of elon- 

 gated cells, invested by others of a rounded, embryonic character, 

 and in all respects similar to embryonic muscle-fibres. The deli- 

 cate cross-striation may be recognised in situ, still better on the 

 isolated fibre (Fig. 249, a). The fibres, which are at first small, 

 containing only one or two nuclei, bear many nuclei later on, and 

 swell up at the ventral end, where a multitude of nuclei are 

 formed by rapid division, and lie all together, while the plasma 

 surrounding the terminal part increases in bulk, and exhibits a 



