It is in this way that I explain the fact that the majority of the caterpillars of the Sphingidæ are absolutely without markings when they emerge from the egg. Thus, for instance, the caterpillars of _Chærocampa_ (Fig. 116, _A_), of _Macroglossa_ (Fig. 115), and of _Deilephila_ (Fig. 118, _A_), as well as those of the _Smerinthus_ species, are at first without stripe or mark of any kind; they are of a pale green colour, almost transparent, and very difficult to recognize when they sit upon a leaf. How very greatly the different stages _can be_ independently adapted to the different conditions of their life, when that is necessary for the preservation of the species, is shown in the most striking manner by many species. Thus the little green caterpillar of _Aglia tau_, when it leaves the egg, bears five remarkable reddish rod-like thorns, which in form and colour resemble the bud-scales of the young beech-buds among which they live, and which disappear later on; the full-grown caterpillar shows nothing of these, but is leaf-green, marked with oblique stripes. Even if the use of these reddish thorns be other than I have indicated, we have in any case to deal with a special adaptation of _one_, and that the first caterpillar-stage, and what can happen at this stage is possible also at every other. Nor is it only animals which undergo metamorphosis that can exhibit independent phyletic variation at every stage, but those also with direct development, and indeed, in the case of these, we may assume adaptation of this kind at almost every stage in the history of the organs, as we have already seen, because the great abridgement of the phylogeny into the ontogeny necessitates a very precise mutual adaptation of the organ-rudiments and of the diverse rates of development. We have thus been led by the facts discussed--and numerous others from other groups in the animal kingdom might be ranked along with them--to two main propositions, which express the relation of phylogeny to ontogeny. The first and fundamental proposition is the one already formulated. The ontogeny arises from the phylogeny by a condensation of its stages, which may be varied, shortened, thrown out, or compressed by the interpolation of new stages. The second proposition refers to individual parts, and may run as follows: As each stage can undergo new adaptations by itself, so can every part, every organ; such new adaptations very often show a tendency to be transferred to the immediately antecedent stage in ontogeny. It is not my intention to formulate the laws of ontogeny just now, otherwise many others might be added to these, such as that of the regular transference of characters acquired at one end of a segmented animal to the other segments: I must confine myself here to bringing the two main propositions into harmony with the principles of our theory of heredity.