I may now add a few explanations which are necessary for understanding the subsequent descriptions. It was found impossible to avoid the introduction of some new technicalities for describing the various elements of larval markings, especially as the latter had to be treated of scientifically. I have therefore chosen the simplest and most obvious designations, all of which have already been employed by various authors, but not in any rigorously defined sense. I understand by the “dorsal line” that which runs down the middle of the back; the lines above and below the spiracles will be respectively distinguished as the “supra-” and “infra-spiracular” lines, and the line between the dorsal and spiracular as the “subdorsal line.” The distinction between “ring-spots” and “eye-spots” will be made manifest in the course of the investigation. A glance at any of the existing descriptions of larvæ will show how necessary it was to introduce a precise terminology. Even when the latter is exact as far as it goes, the want of precise expressions not only makes the descriptions unnecessarily long, but it also considerably increases the difficulty of comparing one species with another, since we can never be sure whether the same designation applies to the same homologous character. For instance, when the larva of _Chærocampa Elpenor_ is said to have “a light longitudinal line on the sides of the thoracic segments,” this statement is indeed correct; but it is not apparent whether the line is above or below, and consequently it does not appear whether it is the equivalent of the longitudinal line “on the sides” of the segments in other species. If, however, it is said that this line is “_subdorsal_ on the thoracic segments, and on the eleventh abdominal segment,” it is thereby indicated that we have here a residue of the same marking which is found completely developed in many other Sphinx-larvæ, and indeed in the young stages of this same species. The mode of describing caterpillars hitherto in vogue is in fact unscientific; the descriptions have not been made with a view to determining the _morphology_ of the larvæ, but simply to meet the practical want of being able to readily identify any species that may be found: even for this purpose, however, it would have been better to have employed a more precise mode of description. I. ONTOGENY AND MORPHOLOGY OF SPHINX-MARKINGS. THE GENUS CHÆROCAMPA, DUPONCHEL. Although by no means in favour of the excessive subdivision of genera, I am of opinion that Ochsenheimer’s genus _Deilephila_ has been correctly separated by Duponchel into the two genera _Chærocampa_ and _Deilephila_, _sensû strictiori_. Such a division may appear but little necessary if we examine the perfect insects only; but the developmental history of the caterpillars shows that there is a wide division between the two groups of species, these groups however being branches of one stem. CHÆROCAMPA ELPENOR, LINN.