Moreover, when in the _Macroglossinæ_ (the genera _Macroglossa_, _Pterogon_, and _Thyreus_) we see precisely the same simple marking (the subdorsal) line retained throughout all the stages in two genera, whilst in the _Smerinthinæ_ this line vanishes at a very early stage, and in the _Sphinginæ_ is only present in traces, we can give but one explanation of these facts. We have here a fragmentary series representing the phyletic development of the Sphinx-markings, which latter have arisen from one original plan--the simple subdorsal line--and have then undergone further development in various directions. As this subsequent development advanced, the older phyletic stages would always be relegated to younger ontogenetic stages, until finally they would be but feebly represented even in the youngest stage (_D. Euphorbiæ_), or else entirely eliminated (most of the species of the genus _Sphinx_). I believe that no other sufficient explanation of these facts can be adduced. Granting that the correctness of the above views can no longer be doubted, we may now take up the certain position that the ontogeny of larval markings reveals their phylogeny, more or less completely, according to the number of phyletic stages omitted, or, in some exceptional cases, falsified. In other words, the ontogeny of larval markings is a more or less condensed and occasionally falsified recapitulation of the phylogeny. Considering this to be established, we have next to deal with the uniformity of the developmental phenomena, from which we may then attempt to trace out the inciting causes underlying this development. The law, or, perhaps better, the line of direction followed by the development, is essentially the following:-- 1. The development commences with a state of simplicity, and advances gradually to one of complexity. 2. New characters first make their appearance in the last stage of the ontogeny. 3. Such characters then become gradually carried back to the earlier ontogenetic stages, thus displacing the older characters, until the latter disappear completely. The first of these laws appears almost self-evident. Whenever we speak of development, we conceive a progression from the simple to the complex. This result therefore does nothing but confirm the observation, that we have actually here before us a development in the true sense of the word, and not simply a succession of different independent conditions.