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Fig. 111.—Fore tibia of Phanæus carnifex, ♂, showing no trace of the tarsus.

Fig. 112.—Fore leg of the mole-cricket: A, outer, B, inner, aspect; e, ear-slit.—After Sharp.

The loss of tarsi may be due to disuse rather than to the inheritance of mutilations. Judging by the enlarged fore tibiæ, which seem admirably adapted for digging, it would appear as if tarsi, even more or less reduced, would be in the way, and thus would be useless to the beetles in digging. Careful observations on the habits of these beetles might throw light on this point. It may be added that the fore tarsi in the more fossorial Carabidæ, such as Clivina and Scarites, as well as those of the larva of Cicada and those of the mole crickets (Fig. 112), are more or less reduced; there is a hypertrophy of the tibiæ and their spines. The shape of the tibia in these insects, which are flattened with several broad triangular spines, bears a strong resemblance to the nails or claws of the fossorial limbs of those mammals which dig in hard soil, such as the armadillo, manis, aardvark, and Echidna. The principle of modification by disuse is well illustrated in the following cases.