This conclusion becomes still more certain on comparing the markings with those of a nearly allied genus; without such comparison the separation of the genus _Macrosila_, Boisd., from _Sphinx_ is scarcely justifiable. If to these two genera we add _Dolba_, Walk., and _Acherontia_, Ochs., we must be principally struck with the great similarity in the markings, which often reaches to such an extent that the differences between two species consist entirely in small shades of colour, while the divergence of the moths is far greater. Of the genera mentioned, I am acquainted altogether with fourteen species of caterpillars:--_Macrosila Hasdrubal_, _Rustica_,[119] and _Cingulata_;[119] _Sphinx Convolvuli_, _Ligustri_, _Carolina_,[119] _Quinquemaculata_,[119] _Drupiferarum_,[119] _Kalmiæ_,[119] and _Gordius_;[119] _Dolba Hylæus_;[119] _Acherontia Atropos_, _Styx_,[120] and _Satanas_.[120] With one exception all these caterpillars possess oblique stripes of the nature of those of the _Smerinthus_ larvæ, and most of them are without any trace of a subdorsal line; one species--the North American _M. Cingulata_--has a completely developed subdorsal; and the typical European species, _S. Convolvuli_, has a rudimentary subdorsal line. The ground-colour in most of these species is of the same green as that of the leaves of their food-plants; some are brown, _i.e._ earth-coloured, and in these the markings do not appear so prominently; others again possess very striking colours (_A. Atropos_), the oblique stripes in these cases being very vivid. Only _M. Hasdrubal_[121] separates itself completely from this system of classification, since this species is deep black with narrow yellow rings, the horn and last segment being red. The large and most striking caterpillar of _M. Hasdrubal_ is the same which Wallace has made use of for his theory of the brilliant colours of caterpillars. The explanation of the origin of this widely divergent mode of marking could only be furnished by the ontogeny, in which one or another of the older phyletic stages will certainly have been preserved. Strictly speaking the same should be said of the other species--nevertheless their comparison with the so similarly marked _Smerinthinæ_, together with the circumstance that in certain species a subdorsal line can be traced, makes it appear correct to suppose that here also the subdorsal was the primary marking, this line being subsequently entirely replaced by the oblique stripes. The _Sphinginæ_ would therefore be a younger group than the _Smerinthinæ_, a conclusion which is borne out by the fact that in the former the oblique stripes have reached a higher development, being always of two, and sometimes even of three colours (_S. Drupiferarum_, white, red, black), whilst in the species of _Smerinthus_ they only occasionally possess uniformly coloured borders. THE GENUS ANCERYX, BOISD.