Trophibiosis, is the relationship between ants on the one hand and aphids, coccids and the like on the other; these species being sought and attended by the ants for their own benefit: see myrmecophily.
Xenobiosis, is where one species of ant lives as a guest in the nest of another, maintaining its own household, and mingling freely with the host species, the two living on terms of mutual toleration.
Symbiotic: species that live together in a state of symbiosis.
Symmetrical: evenly developed on both sides.
Symmetry: that regular arrangement of organs or parts which is capable of division into similar halves or similar radii.
Sympathetic nervous system: applied to the nerves and ganglia of the alimentary canal and sonic other viscera which they innervate; = vagus; visceral nervous system.
Symphily: the relation borne to ants by the true guests which inhabit their nests and are fed and tended: rendering in return some substance or service desired by the ants: see metochy and synechtry.
Symphyla: a group name for apterous species resembling myriapods in appearance, with functional abdominal legs and the genital openings on the last abdominal segment: regarded by some as connecting forms between insects and myriapods, e.g. Scolopendrella.
Symphysis: where two sclerites are joined together by a soft membrane, permitting a slight motion.
Synaptera: originally wingless insects without metamorphosis; the Thysanura.