The _antennæ_, or feelers, are two filamentary organs articulating on each side of the face and above the clypeus. They comprise the _scape_ (_a_), or basal joint, and (_b_) the _flagellum_ or terminal apparatus; the latter consists of closely attached conterminal joints, and usually forms an elbow with the scape; collectively these joints number twelve in the female and thirteen in the male. They are all of various relative lengths, which sometimes aid specific determination. The scape, however, is usually much longer than any of the rest, and in some males has a very robust and even angulated shape. A description of the antennæ always enters into the generic character; they usually differ very materially both in length and form in the sexes. They are often filiform (2), but more generally subclavate (1), and sometimes distinctly so, and where they have the latter structure it is found in both sexes. They constantly differ in the species of a long genus (_Andrena_, _Normada_, _Halictus_). In the male of the genus _Eucera_, they have a remarkable extension, being as long as the body, whereas folded back they are rarely so long, or not longer than the thorax in other males, speaking in reference only to our native kinds. In the females they are not often longer than the head. It is in the males of the genus _Halictus_ that they take the greatest extension. In the male of the genus _Eucera_, we also find the remarkable peculiarity of the integument of some of the joints being distinctly of an hexagonal structure,—a peculiarity often observable in natural structures. In this case it may refer to the sensiferous function of the organ, and to which I shall have occasion to revert when I speak of the senses of our insects. We sometimes find the joints of the antennæ moniliform, something like a string of beads, or with each separate joint forming a curve, or with their terminal one, as in _Megachile_, greatly compressed. The relative lengths of the joints often yield conclusive separative specific characters, and which may be very advantageously made available, especially where other distinctive differences are obscure, and in cases where the practised eye observes a distinction of habit, evidently specific, although it is difficult to seize tangible characteristics. The _trophi_ are the organs of the mouth of the bee collectively. When complete in all the parts, as exemplified in the genus _Anthoptera_, they consist of the _labrum_, or upper lip; the _epipharynx_, or valve, falling over and closing the aperture of the gullet; the _pharynx_, or gullet, which forms the true mouth and entrance to the œsophagus; the _hypopharynx_ which lies immediately below the gullet and assists deglutition; the _labium_, or lower lip, and the true tongue. These parts are all single; the parts in pairs are the _mandibles_, the _maxillæ_, the _maxillary palpi_, the _labial palpi_, and the _paraglossæ_.