The Cockroach is historically one of the most ancient, and structurally one of the most primitive, of our surviving insects. Its immense antiquity is shown by the fact that so many Cockroaches have been found in the Coal Measures, where about eighty species have been met with. The absence of well-defined stages of growth, such as the soft-bodied larva or inactive pupa, the little specialised wings and jaws, the simple structure of the thorax, the jointed appendages carried on the end of the abdomen, and the unconcentrated nervous system, are marks of the most primitive insect-types. The order Orthoptera is undeniably the least specialised among winged insects at least, and within this order none are more simple in structure, or reach farther back in the geological record than the Cockroaches. The wingless Thysanura are even more generalised, but their geological history is illegible.[23] [23] Brongniart has just described a Carboniferous Insect which he considers a Thysanuran (_Dasyleptus Lucasi_), though it has but one anal appendage. See C. R. Soc. Ent., France, 1885. _Life-History._ The eggs of the Cockroach are laid sixteen together in a large horny capsule. This capsule is oval, with roundish ends, and has a longitudinal serrated ridge, which is uppermost while in position within the body of the female. The capsule is formed by the secretion of a “colleterial” gland, poured out upon the inner surface of a chamber (vulva) into which the oviducts lead. The secretion is at first fluid and white, but hardens and turns brown on exposure to the air. In this way a sort of mould of the vulva is formed, which is hollow, and opens forwards towards the outlet of the common oviduct. Eggs are now passed one by one into the capsule; and as it becomes full, its length is gradually increased by fresh additions, while the first-formed portion begins to protrude from the body of the female. When sixteen eggs have descended, the capsule is closed in front, and after an interval of seven or eight days, is dropped in a warm and sheltered crevice. In _Periplaneta orientalis_ it measures about ·45 in. by ·25 in. (fig. 5). The ova develop within the capsule, and when ready to escape are of elongate-oval shape, resembling mummies in their wrappings. Eight embryos in one row face eight others on the opposite side, being alternated for close packing. Their ventral surfaces, which are afterwards turned towards the ground, are opposed, and their rounded dorsal surfaces are turned towards the wall of capsule; their heads are all directed towards the serrated edge. The ripe embryos are said by Westwood to discharge a fluid (saliva?) which softens the cement along the dorsal edge, and enables them to escape from their prison. In _Blatta germanica_ the female is believed to help in the process of extrication.[24] The larvæ are at first white, with black eyes, but soon darken. They run about with great activity, feeding upon any starchy food which they can find.