5. This is also exhibited by all ants that harbor root-aphids and root-coccids in their nests. Not only are these insects kept in confinement by the ants, but they are placed by them on the roots. In order to do this the ants remove the earth from the surfaces of the roots and construct galleries and chambers around them so that the Homoptera may have easy access to their food and even move about at will. 6. Many ants construct, often at some distance from their nests, little closed pavilions or sheds of earth, carton, or silk, as a protection for their cattle and for themselves. The singular habit may be merely a more recent development from the older and more general habit of excavating tunnels and chambers about roots and subterranean stems. 7. The solicitude of the ants not only envelops the adult aphids and coccids, but extends also to their eggs and young. Numerous observers have observed ants in the autumn collecting and storing aphid eggs in the chambers of their nests, caring for them through the winter and in the spring placing the recently hatched plant lice on the stems and roots of the plants. In the foregoing I have discussed the ethological relations of ants to a variety of other organisms. This, however, did not include an account of some of the most interesting symbiotic relations, namely, those of the ants to other species of their own taxonomic group and to termites. This living together of colonies of different species may be properly designated as social symbiosis, to distinguish it from the simple symbiosis that obtains between individual organisms of different species and the intermediate form of symbiosis exhibited by individual organisms that live in ant or termite colonies. The researches of the past forty years have brought to light a remarkable array of instances of social symbiosis, varying so much in intimacy and complexity that it is possible to construct a series ranging from mere simultaneous occupancy of a very narrow ethological station, or mere contiguity of domicile, to an actual fusion, involving the vital dependence or parasitism of a colony of one species on that of another. Such a series is, of course, purely conceptual and does not represent the actual course of development in nature, where, as in the animal and vegetable kingdoms in general, development has not followed a simple linear course, but has branched out repeatedly and terminated in the varied types at the present time.