SummaryAttention is especially directed to two aspects of the relations between preyer and preved upon.First, that there are many factors which determine whether or not, at any particular time, one animal will prey upon another, of which relative palatability is only one. In order, therefore, to demonstrate a difference in palatability between various foods, all these determining factors must be taken into account,Second, that observations indicate that both birds and fish are deluded by rough resemblances to the insects upon which they are at the time feeding.