_Stage 4._--Open ring-spots appear on the subdorsal line on all the segments from the eleventh to the first. _D. Zygophylli_ and the North American _D. Lineata_ belong here.
_Stage 5._--Closed ring-spots are situated on the subdorsal line. Of the known species, only _D. Livornica_ concludes its development at this phyletic stage.
_Stage 6._--A single row of ring-spots replaces the subdorsal line. _D. Galii_, _Vespertilio_, and _Mauritanica_ represent this stage at the conclusion of their ontogeny.[95]
_Stage 7._--A double row of ring-spots. Only _D. Dahlii_, _Euphorbiæ_, and _Nicæa_ attain to this highest stage of _Deilephila_ marking, the two first species in the fourth stage, and _Nicæa_ in the third stage of its ontogeny.
Although our knowledge of the history of the development of the individual species is still so fragmentary, we may conclude with certainty that the development of the markings has been uniform throughout--that it has proceeded in the same manner in all species. All the species appear to be making for the same goal, and the question thus arises whether there may not be an innate force urging their phyletic development. The rigorous examination of this conception must be reserved for a later section. Here, as we are only occupied essentially in establishing facts, it must be remarked that retrogression has never been observed. The young larval forms of a species never show the markings of a later phyletic stage than the older larval forms; the development takes the same course in all species, only making a greater advance in the same direction in some than in others.
Thus, _Nicæa_ and _Euphorbiæ_ have advanced to the seventh phyletic stage, _Zygophylli_ and _Hippophaës_ only to the third, and some specimens of _Zygophylli_ to the fourth. But at whatever phyletic stage the ontogeny of a species may terminate, the young larval stages always display the older phyletic stages. Thus, _Galii_ in its last ontogenetic stage reaches the _sixth_ phyletic stage; in its penultimate stage it reaches the _fifth_ phyletic stage; and in its third stage; the _fourth_ phyletic stage is represented, so that little imagination is required to anticipate that in the second stage the _third_ or _second_ phyletic stage would be pictured.