THERE is a story which redounds to the sagacity of a certain Dutch farmer, who, on the sudden appearance of herrings in the ditches on his property, sold it, on account of the indisputable evidence which such fish afforded, of the leaky condition of the dykes. The Dutchman's inference will serve to indicate how much surprise the discovery of jelly-fish in Lake Tanganyika, by Dr. Boehm, created in the minds of those who were interested in the past history of the great lakes in Africa, for, in the presence there even of a single organism so typically, marine, and so unlike any real fresh-water form as a medusa, there was as good, indeed far better, evidence for the former access of the sea to those regions, than that which was afforded by the herrings in the Dutchman's ditch.