In the _eyes_, or _stemmata_, this diversity is less remarkable. Latreille has described two ants, _Formica contracta_ and _coeca_, in the neuter of which he could discover no eyes[805]: in the former, the female, however, had large ones. The male he appears not to have known, but it probably was not destitute of these organs; of the latter he was acquainted only with the workers. The neuter of _Myrmica rubra_, another ant, has no ocelli or stemmata, although the male and female are provided with them[806]. They are discoverable only in the former sex of that singular insect related to the ants, _Mutilla europæa_. Other insects differ in the _size_ of the eyes of their sexes. In the hive-bee, and some _Ephemeræ_, the eyes of the drone or male are much larger than those of the worker and female, and also meet at the vertex, having their stemmata below the conflux; whereas in these latter they are widely distant[807]. In _Stratyomis_, _Tabanus_, and many other two-winged flies, the _male_ eyes meet at some point below the stemmata, and above the antennæ. In the former they touch more at an angle; for the vertex forming a narrow isosceles triangle, and for the anterior part of the face one nearly equilateral: while those of the _female_ are separated by a considerable interval. In _Heptatoma_ and _Hæmatopota_ in that sex, a similar interval obtains; while in the other, after forming a minute short triangle, they unite for a considerable space, and then diverging, form the face. This is also the case in _Tabanus_; but in the female, the space that intervenes between the posterior part of the eyes is much narrower than in these two cognate genera of the horse-flies. In some others of this order, as _Musca_ Latr., the eyes of the male do not touch, but approach posteriorly much nearer to each other than those of the other sex. In a few instances the sexes vary even in the number of their eyes, as well as the size. This occurs in some species of _Ephemera_ L. (_E. diptera_, &c.), in which the male, besides the common lateral ones, has two large and striking intermediate eyes, that sit upon vertical pillars or footstalks[808].
2. The _Trunk_. The thorax of many coleopterous males, especially of the _Dynastidæ_ and _Copridæ_ amongst the petalocerous tribes, exhibits very striking differences from that of the female. In many _Lucani_ the lateral angle is more prominent. In _Anthia_ it is bilobed posteriorly, while in the last-mentioned sex it is entire[809]. In _Phanæus carnifex_ MacLeay (_Copris_ F.) it is elevated into a plane triangular space, with the vertex of the triangle pointing to the head; but in the female it is convex, with an anterior abbreviated transverse ridge[810].