But the most peculiar wings in the family are the folded structures found in some forms of the groups Ectobiides and Oxyhaloides [Anaplectinae and Plectopterinae of de Saussure]. These have been studied by de Saussure,[150] and in Fig. 123 we reproduce some of his sketches, from which it will be seen that in B and C the wing is divided by an unusual cross-joint into two parts, the apical portion being also longitudinally divided into two pieces _a_ and _b_. Such a form of wing as is here shown has no exact parallel in any of the other groups of Insects, though the earwigs and some of the Coleoptera make an approach to it. This structure permits a very perfect folding of the wing in repose. The peculiarities exhibited have been explained by de Saussure somewhat as follows. In the ordinary condition of Orthoptera the axillary or anal field (P) when the wings are {227}closed collapses like a fan, and also doubles under the anterior part (H) of the wing along the line _a a_, in Fig. 123, A, the result being similar to that shown by our Fig. 124. It will be noticed in Fig. 123, A, that a small triangular area (_t_) exists at the tip of the wing just where the fold takes place, so that when the wing is shut this little piece is liberated, as shown in _t_, Fig. 124. In many Blattidae, e.g. _Blabera_ (Fig. 132), no trace of this little intercalated piece can be found, but in others it exists in various degrees of development intermediate between what is shown in _Thorax porcellana_ (Fig. 123, A) and in _Anaplecta azteca_ (123, B), so that _a_, _b_ of the latter may be looked on as a greater development of the condition shown in A at _t_. It will be noticed that the superadded part of the wing of 123, B, possesses no venation, being traversed only by the line along which it folds; but in the wing of _Diploptera silpha_, 123, C, the corresponding part is complexly venated. This venation, as Brunner says,[151] is not an extension of the ordinary venation of the wing, but is _sui generis_. It is curious that though all the degrees of development between A and B exist in various forms of the tribes Ectobiides and Oxyhaloides, yet there is nothing to connect the veined apex of Diploptera with the unveined one of _Anaplecta_. [Illustration: FIG. 123.—Hind wings of Blattidae. A, _Thorax porcellana_; B, _Anaplecta azteca_; C, _Diploptera silpha_. (After de Saussure.)] [Illustration: FIG. 124.—Hind wing of _Blatta_ folded. _t_, Free triangular area. (After de Saussure.)] The internal anatomy of Blattids has been investigated in only one or two species. There are no great peculiarities, but some features of minor interest exist. The alimentary canal (Fig. 125) is remarkable {228}on account of the capacious crop, and the small gut-like, chylific ventricle; eight elongate pouches are situate on this latter part at its junction with the gizzard.