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Rh the Hymenoptera from the rest of their class, but it is necessary to describe the various parts more in detail.

The head is not received into a cavity of the thorax, but is attached to it by a ligament, so flexible that the head can be almost turned round upon it. It is likewise capable of some extension, and the head has thereby considerable freedom of motion. The composite eyes are sometimes larger in the males than in the other sex. The stemmata are always three in number, commonly disposed in an equilateral triangle, but occasionally almost in a transverse line. In the organs of the mouth we can distinctly recognise mandibles, maxillæ, lingua, labrum, labium, and palpi; but these parts are so variously modified in different tribes, that a general definition of them will possess little value. The mandibles are strong and salient, usually toothed, and sometimes each blade appears as if formed by the union of two similar pieces. The maxillæ are usually much developed, the blade or stipes often greatly elongated, and the insertion (the cardo or hinge of Kirby,) distinctly visible. The blade of the maxillæ acts an important part in composing the tube in honey-sucking tribes. There are commonly two lobes at the extremity, which are sometimes acute, at other times very obtuse. The palpi attached to this blade are almost always long, and in the greater number of instances contain six joints; in the minute parasites, however, they are frequently abnormal, and often present only two articulations. The labium is much larger than