mental character which profoundly influences their habits and their modes of reaction to bodily and external impressions. Among the mammalia other than man and possibly apes and monkeys, gregariousness is found in two broadly distinguishable types according to the function it subserves. It may be either protective as in the sheep, the deer, the ox, and the horse, or aggressive as in the wolf and allied animals. In both forms it will involve certain common types of capacity, while the distinguishing characteristic of each will be a special kind of reaction to certain stimuli. It is important to understand that these peculiarities are possessed by each individual of the larger unit, and will be displayed by him in a characteristic way whether he is in the company of his fellows or not. It is not necessary to repeat here in any detail the characters of the gregarious mammal. They have been dealt with in an earlier essay, but it is desirable to emphasize here certain features of exceptional importance and some which were but little discussed before.
The quite fundamental characteristic of the social mammal, as of the bee, is sensitiveness to the voice of his fellows. He must have the capacity to react fatally and without hesitation to an impression coming to him from the herd, and he must react in a totally different way to impressions coming to him from without. In the presence of danger his first motion must be, not to fly or to attack as the case may be, but to notify the herd. This characteristic is beautifully demonstrated in the low {109} growl a dog will give at the approach of a stranger. This is obviously in no way part of the dog’s programme of attack upon his enemy—when his object is intimidation he bursts into barking—but his first duty is to put the pack on its guard. Similarly the start of the sheep is a notification and precedes any motion of flight.
In order that the individual shall be sensitive in a special degree to the voice of the herd, he must have developed in him an infallible capacity for