[Read before the Nelson Philosophical Society, 2nd September, 1925; received by Editor, 10th September, 1925; issued separately, 22nd February, 1927.]
The object of the present paper is to describe and figure the maxillae in all groups of which material has been available for study. Owing, however, to the limited nature of the lepidopterous fauna of New Zealand, the investigation must necessarily have proved very incomplete were it not that, through the kindness of correspondents I have been able to study a fair number of forms from other regions. Though all the parts of the maxilla will be dealt with, the chief interest will centre in the maxillary palpi. In systematic works on the Lepidoptera, we frequently find it stated that in this or that group the maxillary palpi are absent. In many of these instances, however, careful examination will show that though the organs are extremely minute and vestigial, they are still to be found.
The general structure of the maxillae will now be briefly described, in order that the nomenclature applied to the various parts may be clearly understood. The first maxilla in the most generalized Lepidoptera consists of the following parts. (1) The Cardo, a more or less horizontally placed small basal piece, often somewhat triangular in shape. (2) The Stipes, a usually well developed sclerite following the cardo, generally longer than broad. (3) The Maxillary Palp, a four- or five-segmented appendage rising from the apical outward area of the stipes. (4) The Galea, a weakly chitinized irregularly cone-shaped structure springing from the central portion of the apex of the stipes; in all except the most primitive families the galeae are modified to form an elongated suctorial organ, the haustellum or tongue. (5) The Lacinia, a small pointed organ fused basally with the galea; in all but the Micropterygidae this organ is absent. Without dissection the cardo can seldom be seen; the stipes is usually at least partially visible; the galeae, when developed into the haustellum, become prominent, and can be seen in part even in the more primitive state; the palp, when reduced, is frequently completely hidden,
but when consisting of several segments it may come into view by hanging downwards clear of the other mouth-parts or by being curved upwards till it rests above the labial palp; the lacinia is always hidden. Certain parts which are present in some of the other orders of insects are not definitely recognizable in the Lepidoptera. These are the subgalea, a sclerite lying on the inner side of the stipes, and the digitus, or finger, a small structure forming a second segment to the lacinia. There is also the palpifer, a pedestal on which the maxillary palp articulates, but in the Lepidoptera this structure, when present, appears as an outgrowth of the stipes; it is, however, at times so prominent that it might easily be mistaken for the basal segment of the palp. Figures giving front and back views (or from above and beneath) of the head of Sabatinca incongruella (Walk.) are shown, in order to display the mouth parts as they appear in situ. These figures, in common with all the others, have been drawn with the aid of a camera lucida from material macerated in a ten per cent. solution of KOH.
A detailed description of the maxilla, from its primitive condition in the most generalised types to its specialised forms in the higher families, will now follow.