- Electric rays (genus Torpedo) can deliver electric shocks to stun their prey and to discourage predators. The voltage is produced by thin, waferlike cells called electrocytes, each of which acts as a battery with an emf of about 10-4 V. Stacks of electrocytes are arranged syde-by-side on the underside of Torpedo. In such a stack, the positive face of each electrocyte touches the negative face of the next electrocyte. What is the advantage of stacking the electrocytes? Of having the side by side?
the advantage of stacking them (placing the cells in series) is that then the individual cell voltages add. This allows the animal to generate a high enough voltage to stun or even kill its prey.
If placed side by side (in parallel) then the cell currents add but the voltages do not, and the shock would not be lethal.
The electrocytes are like tiny batteries. Like batteries, if you stack them so the positive terminal of one is connected to the negative terminal of the next one, their voltages add up. Hence, if you stack 1,000 electrocytes, each having 0.15 V, the result is 150V. That will be enough to kill, as long as the battery can supply sufficient current. In the case of electric eels and rays, that is indeed the case.