Fig. 53—Abdomens of ants. A, Of Camponotus rubripes (Formicides); B, of Ectatomma auratum (Ponerides); C, of Aphaenogaster barbara (Myrmicides). a, Propodeum; b, first abdominal segment forming a scale or node; c, second; d, third abdominal segment.
In ants the distinction between the three great regions of the body is very marked. The abdomen is connected with the propodeum in a peculiar manner, one or two segments being detached from the main mass to form a very mobile articulation. This is the most distinctive of the characters of ants. The structure and form of these parts varies greatly in the family: and the Amblyoponides do not differ in a marked manner from the Scoliidae in fossorial Hymenoptera.
Fig. 54—Front of head of Dinoponera grandis. A, Mouth closed; B, open.
The arrangement of the parts of the mouth is remarkable, and results in leaving the mandibles quite free and unconnected with the other trophi; the mouth itself is, except during feeding, closed completely by the lower lip and maxilla assuming an ascending vertical direction, while the upper lip hangs down and overlaps the lower lip, being closely applied to it; so that in Ponerides the palpi, except the apices of the maxillary pair, are enclosed between the upper and lower lips (Fig. 54, A). In Cryptocerini the palpi are not covered by the closed lips, but are protected by being placed in chinks at the outsides of the parts closing the mouth. The mandibles of ants can thus be used in the freest manner without the other parts of the mouth being opened or even moved. The mandibles close transversely over the rest of the mouth, and when shut are very firmly locked. There are, however, some ants in which the lips remain in the position usual in mandibulate Insects.
The antennae, except in the males of some species, have a long basal joint and are abruptly elbowed at its extremity. The eyes and ocelli vary excessively, and may be totally absent or very highly developed in the same species. The winged forms are, however, never blind. The size of the head varies extremely in the same species; it is frequently very small in the males, and largest in the workers. In some ants the worker-caste consists of large-headed and small-headed individuals; the former are called soldiers, and it has been supposed that some of them may act the part of superior officers to the others. It should be clearly understood that there is no definite distinction between soldiers and workers; so that in this respect they are widely different from Termites.
Fig. 55—Oecodoma cephalotes. South America. A, Worker major; B, female after casting the wings.
Fig. 56.—Stridulating organ of an ant, Myrmica rubra, var. laevinodis. Sagittal section of part of the 6th and 7th post-cephalic segments. (After Janet.) a, a1, muscles; b, connecting membrane (corrugated) between 6th and 7th segments: c, 6th segment; d, its edge or scraper; e, striate area, or file on 7th segment; f, posterior part of 7th segment; g, cells, inside body; h, trachea.