It was that that saved me.
"Look out, King!" I warned.
Exactly as I spoke I set my foot on a yielding stone trap-door--felt a blast of cool air--and heard water unmistakably.

The air brought a stagnant smell with it.

I slid forward and downward, but sprang simultaneously, managing to get my fingers on the edge of the stone in front.

But the balanced trap-door, resuming its equilibrium, caught me on the back of the head, half-stunning me, and in another second I would have gone down into the dark among the alligators.

I just had enough consciousness left to realize that I was hanging over the covered end of the alligator tank.
But the faint outer circle of light cast by the Mahatma's lantern just reached me, and as King turned his head to acknowledge my warning he saw me fall.