[April 28th 1916]
main body moved. I think, as might have been expected, that the locusts in the upper and lower strata were more liable to go astray than those in the centre of the swarm. It was also evident that the locusts in the lower strata of the migrating stream often travelled at a faster speed than those in the upper strata, and, when the swarm wheeled or tended to change its course, the lower and upper strata could be seen to move in opposite directions. In fact, though the surmise may be absolutely wrong, it seemed to me that the swarm consisted of a series of layers ot strata of insects, and that the movements of all the locusts in one layer were identical and in unison one with the other, but were to some extent independent of the movements of the locusts in the other layers.