EFFECTOR MECHANISMS 



397 



In the torpedo they are supplied by branches of the vagus nerve which arise 

 in large lobes of the medulla oblongata; in the skate the nervous supply is 

 derived from ventral roots of spinal nerves. The terminal nervous arboriza- 

 tion closely invests one surface of the electroplate (Fig. 9.18). Surrounding 

 the electroplates are connective tissue, intercellular fluid and blood vessels. 

 Present evidence indicates that each electroplate is a modified muscle 

 fibre, with the development of an electrical potential as its chief physio- 

 logical function ; the innervated surface of the electric plate would thus 

 correspond to a motor end-plate (57, 58). 



During discharge each electroplate generates a small voltage (about 

 150 mV in Electrophorus) and the electrical potentials of the separate 



Fig. 9.18. Longitudinal Section through an Electrical Plate of Raja batis 



g, nerve fibres passing to plate ; a-f, parts of electric plate (a, outer protoplasmic and 

 nuclear layer; b, striated layer; c, alveolar layer; d, stem of disc; e, striated zone of disc; 

 /, posterior gelatinous cushion), s, septum. (After Ewart, 1889.) 



electroplates summate. The dorsal surface of the organ is positive in the 

 torpedo, and the current travels through the organ from the ventral to the 

 dorsal surface. Thus, the columns of electroplates discharge in parallel, 

 whereas the electroplates within each column act in series. Voltages de- 

 veloped by Torpedo occidentalis on open circuit, and with known external 

 resistances, have been measured. The total peak voltage (measured without 

 external resistance) lies between 20-30 V; that developed on open circuit 

 reaches 220 V. Current output has been calculated for various external 

 shunts, and has been found to increase as the voltage decreases, in a linear 

 relationship. Calculated maximal current values are about 4 A in Narcine 

 brasiliensis and 60 A in T. nobiliana. Maximal power developed at peak of 

 discharge amounts to 10-35 W in Narcine, and 3-6 kW in Torpedo. 



