first, only stretching its neck further over the edge of the table. He several times reiterated his experiment, and always with the same result. Later the two colonies were shut up together in a glass case, and gradually learned to agree. At other times, however, warlike ants show great and needless cruelty to one another:-- They slowly pull from their victim, that is rendered defenceless by wounds, exhaustion, or terror, first one feeler and then the other, then the legs one after another, until they at last kill it, or pull it in a completely mutilated and helpless condition to some out-of-the-way spot where it perishes miserably. Yet some compassionate hearts are to be found among the victors, which only pull the conquered to a distant place in order to get rid of them, and there let them go without injuring them. The following account is also taken from Büchner's 'Mind in Animals,' p. 87:-- The doors are often guarded by special sentries, which fulfil their important duty in various ways. Forel saw a nest of the _Colobopsis truncata_, the two or three very small round openings of which were watched by soldiers, arranged so that their thick cylindrical heads stopped them up, just as a cork stops up the mouth of a bottle. The same observer saw the _Myrmecina Latreillei_ defend themselves against the invasions of the slave-making _Strongylognathus_, by placing a worker at each of the little openings of the nest, which quite stops up the opening either with its head or abdomen. The _Camponotus_ species also defend their nests by stretching their heads in front of the openings, drawing back the antennæ. Each approaching enemy thus receives a sharp blow or bite delivered with the whole weight of the body. MacCook noticed in the nests of the soon to be described Pennsylvanian mound-building ants, the employment of special sentries, which lay watching within the nest entrances, and sprang out at the first sight of danger to attack the enemy; and it was wonderful to see with what swiftness the news of such an alarm spread through the nest, and how the inhabitants came out _en masse_ to meet the enemy. The _Lasius_ species defend their large, strong, and very extensive nests against hostile attack or sieges with equal courage and skill, while other timid species seek to fly as speedily as possible with their larvæ, pupæ, and fruitful queens. There is, as Forel tells us, a regular barricade fight. Passage after passage is stopped and defended to the uttermost, so that the assailants can only advance step and step. Unless the latter are in an enormous majority, the struggle may last a very long time with these tactics. During this time, other