If, from the form possessed by many of the caterpillars of the _Sphingidæ_ on their emergence from the egg, we may venture to draw a conclusion concerning the oldest phyletic stage, these larvæ were originally completely destitute of marking. The characteristic caudal horn must be older than the existing markings, since it is present in the younger stages (except in cases where it is altogether wanting), and is generally even larger than at a later age. There is, however, further evidence that there were once Sphinx-larvæ without any markings. Such a species now exists. I do not mean the boring caterpillars of the _Sesiidæ_,[160] which live in the dark, and are therefore colourless, but I refer to a large larva (over six centimeters long) preserved in spirit in the Berlin Museum,[161] which, from its form, belongs to the _Smerinthus_ group. It possesses a caudal horn, and on the whole upper surface is covered with short and sparsely scattered bristles, such as occur in the _Sesiidæ_. The colour of this unknown insect appears to have been light green, although it now shows only a yellowish shade. Every trace of marking is absent, and it thus corresponds exactly with the youngest stages of the majority of the existing Sphinx-larvæ--even to the short bristles sparsely scattered over the whole upper surface of its body. We have therefore, so to speak, a living fossil before us, and it would be of great interest to ascertain its history. All the data furnished by the developmental history go to show that of the three kinds of markings which occur in the _Sphingidæ_, viz., longitudinal and oblique stripes and spots, the first is the oldest. Among the species which are ornamented with oblique stripes or spots there are many which are longitudinally striped in their young stages, but the reverse case never occurs--young larvæ never show spots or oblique stripes when the adult is only striped longitudinally. The first and oldest marking of the caterpillars of the _Sphingidæ_ was therefore the longitudinal striping, or, more precisely speaking, the subdorsal, to which dorsal and spiracular lines may have been added. That this second stage of phyletic development has also been preserved in existing species has already been sufficiently shown; the greater portion of one group, the _Macroglossinæ_, has indeed remained at this stage of development. From the biological value which must be attributed to this kind of marking, its origination by natural selection presents no difficulty. The first rudiments of striping must have been useful, since they must have broken up the large surface of the body of the caterpillar into several portions, and would thus have rendered it less conspicuous to its enemies.