The variety of shape and external appearance in this family is very great; de Saussure considers it to be a mimetic group. In certain species some parts of the body—more especially the tegmina—have very much the appearance of foliage, and usually in such cases this appearance is confined to the female, the males in this family having, as we have said, the organs of flight more transparent and colourless; in the former sex the alar organs, when present, are frequently but little adapted for flying. In some species the prothorax is expanded at the sides (Fig. 135, _Deroplatys sarawaca_; and Fig. 143, _Choeradodis cancellata_), and in such cases the outline of the natural thorax—if we may use such an expression—may be detected occupying the middle of the unusual expansion. The European _Mantis religiosa_ varies much in colour; in some examples the tegmina are leaf-green, while in others they are brown or gray. There is some evidence extant making it probable that in some species the colour of an individual changes at different times—Colonel Bowker saying of {253}_Harpax ocellata_ that it "beats the Chameleon hollow in changing colour." Some of the species of the old genus _Eremiaphila_ (Fig. 144) are of very unusual form. De Saussure considers that some species of this genus are more highly modified than any other animals for maintaining their existence in desert regions. They are said to be found in places where no vegetation exists, and to assimilate in appearance with the sandy soil, the species varying in colour, so that the individuals agree in tint with the soil on which they dwell. These Insects are referred to the group Orthoderides, and have a short prothorax, the alar organs being unsuited for flight. What they live on is not actually known; although other Insects are the natural food of Mantids, it is said that these desert-frequenting species occur in spots where no other Insect life is known to exist. Lefebvre[181] met with these Eremiaphilas in the desert between the Nile and the Northern Oasis, El Bahryeh, but was quite unable to discover their mode of subsistence. These Insects are very rare in collections, and the information we possess about them is very meagre. [Illustration: FIG. 144.—_Eremiaphila turcica._ (After Westwood.)] Mr. Graham Kerr found on the Pilcomayo river a species of Mantidae living on branches of trees amongst lichens, which it so exactly resembled that it was only detected by the movement of a limb; it was accompanied by a Phaneropterid grasshopper, which bore a similar resemblance to the lichens. One of the rarest and most remarkable forms of Mantidae is the genus _Toxodera_, in which the eyes project outwards as pointed cones (Fig. 145). These Insects offer an interesting problem for study, since we are entirely ignorant about them. Brunner places the Toxoderae in his tribe Harpagides, but with the remark that "these Insects of antediluvian shapes differ essentially from all other Mantidae."