Although much work has been done on the embryology of Blattidae, the subject is still very incomplete. The recent memoirs of Cholodkovsky[165] on _Phyllodromia germanica_ contain so much of general interest as to the development of the external parts of the body that we may briefly allude to them. The earliest appearance of segmentation appears to be due to the centralisation of numerous {238}cells round certain points in the ventral plate. The segmentation of the anterior parts is first distinct, and the appearance of the appendages of the body takes place in regular order from before backwards, the antennae appearing first; the mandibles, however, become distinct only subsequent to the maxillae and thoracic appendages. There are in the course of the development appendages to each segment of the body (he counts eleven abdominal segments); the cerci develop in a similar manner to the antennae; the first pair of abdominal appendages—at first similar to the others—afterwards assume a peculiar stalked form. The abdominal appendages subsequently disappear, with the exception of the ninth pair, which form the ventral styles, and the eleventh pair, which become the cerci. The last ventral segment is said to be formed by the union of the tenth and eleventh embryonic ventral segments. [Illustration: FIG. 133.—A, Tegmen(?) of _Palaeoblattina douvillei_; B, of _Etoblattina manebachensis_. (After Brauer and Scudder.)] As regards their Palaeontological forms Blattidae are amongst the most interesting of Insects, for it is certain that in the Carboniferous epoch they existed in considerable number and variety. A still earlier fossil has been found in the Silurian sandstone of Calvados; it consists of a fragment (Fig. 133, A), looking somewhat like an imperfect tegmen of a Blattid; it was described by Brongniart under the name of _Palaeoblattina douvillei_, and referred by him, with some doubt, to this family. Brauer has, however, expressed the opinion[166] that the fragment more probably belonged to an Insect like the mole-cricket, and in view of this discrepancy of authorities we may be pardoned for expressing our own opinion to the effect that the relic has no connexion with the Insecta. The figure given by Scudder[167] has not, however, so uninsect-like an appearance as that we have copied from Brauer. Whatever may prove to be the case with regard to _Palaeoblattina_, it is certain, as we {239}have already said, that in the Palaeozoic epoch Insects similar to our existing cockroaches were abundant, their remains being found in plenty in the coal-measures both of Europe and North America. Fig. 133, B, shows a fossil tegmen of _Etoblattina manebachensis_ from the upper Carboniferous beds of Ilmenau in Germany. It will be noticed that the disposition of the nervures is very much like that which may be seen in some of our existing Blattidae (cf. the tegmen of _Blabera_, Fig. 132, A), the vena dividens (_a_) being similarly placed, as