STRUCTURE OF IMAGO.—The head of a Lepidopteron is in large part made up of the compound eyes; in addition to these it frequently bears at the top a pair of small, simple eyes so much concealed by the scales as to cause us to wonder if seeing be carried on by them. The larger part of the front of the head is formed by the clypeus, which is separated by a well-marked line from the epicranium, the antennae being inserted on the latter near its point of junction with the former. There is sometimes (_Saturnia_, _Castnia_) on each side of the clypeus a deep pocket projecting into the head-cavity. The other parts of the head are but small. The occipital foramen is very large.[164] [Illustration: Fig. 158—External structure of a female butterfly, _Anosia plexippus_. (After Scudder.) _a_, Base of antenna; _b_, pronotum; _b^2_, scutum of mesothorax; _c_, clypeus; _cx_, coxa; _d_, scutellum; _d^1_, scutellum of metathorax; _e_, post-scutellum (= base of phragma); _em_, epimeron; _ep_, episternum; _f_, scutum of metathorax; _m_, basal part of proboscis (= maxilla); _o_, eye; _p_, labial palp; _r_, mesosternum; _s_, prothoracic spiracle; _t_, tegula; _tr_, trochanter; 1-9, dorsal plates of abdomen.] The antennae are always conspicuous, and are very various in form; they are composed of numerous segments, and in the males of many species attain a very complex structure, especially in Bombyces and Psychidae; they doubtless function in such cases as sense-organs for the discovery of the female. The largest and most important of the mouth-parts are the maxillae and the labial palpi, the other parts being so small as to render their detection difficult. The labrum is a very short, {308}comparatively broad piece, visible on the front edge of the clypeus; its lateral part usually forms a prominence which has often been mistaken for a mandible; Kellogg has applied the term "pilifer" to this part. In the middle of the labrum a small angular or tongue-like projection is seen just over the middle of the base of the proboscis; this little piece is considered by several authorities to be an epipharynx. [Illustration: Fig. 159—Mouth of Lepidoptera. Tiger-moth, _Arctia caja_. A, Seen from front; B, from front and below, _a_, Clypeus; _b_, labrum; _c_, epipharynx; _d_, mandibular area; _d′_, prominence beneath mandibular area; _e_, one side of haustellum or proboscis; _f_, maxillary palp; _g_, labial palp.]