4. _Eye-spots and Ring-spots._--These markings, besides among the _Sphingidæ_, are found only in a very few caterpillars, such as certain tropical _Papilionidæ_ and _Noctuæ_. I know nothing of the conditions of life and habits of these species, however, and without such knowledge it is impossible to arrive at a complete explanation. With Darwin, I take an eye-spot to be “a spot within a ring of another colour, like the pupil within the iris,” but to this central spot “concentric zones” maybe added. In the _Chærocampa_ larvæ and in _Pterogon Œnotheræ_, in which complete ocelli occur, there are always three zones--a central spot, the pupil, or, as I have called it, the “nucleus;” then a light zone, the “mirror;” and, surrounding this again, a dark zone (generally black), the “ground-area.” As ring-spots I will consider those ocelli which are without the nucleus (pupil), and which are not therefore, strictly speaking, deceptive imitations of an eye, but present a conspicuous light spot surrounded by a dark zone. Between these two kinds of markings there is, however, no sharp boundary, and morphologically they can scarcely be separated. Species with ring-spots sometimes have nuclei, and ocellated larvæ in some cases possess only a pale spot instead of a dark pupil. I deal here with the two kinds separately, because it happens that they appear in two distinct genera, in each of which they have their special developmental history. Ring-spots originate in a different position, and in another manner than eye-spots; but it must not, on this account, be assumed without further inquiry, that they are called into existence by the same causes; they must rather be investigated separately, from their origin. Eye-spots are possessed by the genera _Chærocampa_ and _Pterogon_; ring-spots by the genus _Deilephila_. In accordance with the data furnished by the above-given developmental histories, the origination of these markings in the two genera may be thus represented:-- In the genera named, eye-spots and ring-spots are formed by the transformation of single portions of the subdorsal line. In _Chærocampa_ the primary ocelli originate on the fourth and fifth segments by the detachment of a curved portion of the subdorsal, this fragment becoming the “mirror,” and acquiring a dark encircling zone (“ground-area”). The nucleus (pupil) is added subsequently. In _Deilephila_ we learn from the development of _D. Hippophaës_, that the primary annulus arises on the segment bearing the caudal horn (the eleventh) by the deposition of a red spot on the white subdorsal line, which is somewhat enlarged in this region. The formation of a dark “ground-area” subsequently occurs, and with this, at first the partial, and then the complete, detachment of the mirror-spot from the subdorsal line takes place.