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Rh possible by pushing down the magnet; but you see how wildly the spot careers about on the scale when the keeper touches the fish. If we had time, we might cause the fish to stimulate a muscle in the frog-interrupter, and thus ring the bell. This is the method adopted by Professor du Bois Reymond in his investigations on electric fishes. If the keeper wishes it, we can easily fit up an arrangement in the Zoological Gardens by which the fish can ring him up at any time, say when he wants his dinner! I see by the keeper's face that this does not meet with his approbation: a bell at one end of a wire and a gymnotus at the other might almost be as troublesome an arrangement as a telephone in one's bedroom. We are much obliged to Mr. Sclater for lending the fish, and we hope the gymnotus will have a safe journey to his warm tank in the "Zoo."

Time warns me, however, that I must be drawing to a close. We have been trying in these lectures to get an insight into the hidden machinery connected with animal motion. Up to this point, we have only been discussing the mechanism of each individual wheel and pinion, and we have not considered the machine