Again in _Aphis_, the embryology of which has been so well worked out by Huxley,[18] the case is very similar, although the legs are somewhat later in making their appearance. When the young was 1/140th of an inch in length, he found the cephalic portion of the embryo beginning, he says, “to extend upwards again over the anterior face of the germ, so as to constitute its anterior and a small part of its superior wall. This portion is divided by a median fissure into two lobes, which play an important part in the development of the head, and will be termed the ‘procephalic lobes.’ I have already made use of this term for the corresponding parts in the embryos of Crustacea. The rudimentary thorax presents traces of a division into three segments; and the dorso-lateral margins of the cephalic blastoderm, behind the procephalic lobes, have a sinuous margin. It is in embryos between this and 1/100th of an inch in length, that the rudiments of the appendages make their appearance; and by the growth of the cephalic, thoracic, and abdominal blastoderm, curious changes are effected in the relative position of those regions.” In _Chrysopa oculata_, one of the Hemerobiidæ, Packard has described[19] and figured a stage in which the body segments have made their appearance, but in which he says “there are no indications of limbs. The primitive band is fully formed, the protozorites being distinctly marked, the transverse impressed lines indicating the primitive segments being distinct, and the median furrow easily discerned.” Here also, again, the dorsal walls are incomplete, and the internal organs as yet unformed. In certain Dragon-flies (_Calepteryx_), and _Hemiptera_ (_Hydrometra_), the legs, according to Brandt,[20] appear at a still earlier stage. According to the observations of Kölliker,[21] it would appear that in the Coleopterous genus _Donacia_ the segments and appendages appear simultaneously. Kölliker himself, however, frankly admits that “meæ de hoc insecto observationes satis sunt manca,” and it is possible that he may never have met with an embryo in the state immediately preceding the appearance of the legs; especially as it appears from the observations of Kowalevski that in _Hydrophilus_ the appendages do not make their appearance until after the segments.[22] On the whole, as far as we can judge from the observations as yet recorded, it seems that in Homomorphous insects the ventral wall is developed and divided into segments, before the appearance of the legs; but that the latter are formed almost simultaneously with the cephalic appendages, and before either the dorsal walls of the body or the internal organs. [Illustration: FIG. 32.—Egg of _Pholcus opilionides_ (after Claparède).]