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Haase regarded these appendages, from their late development and frequent reduction, as old inherited appendages which are approaching atrophy through disuse.

Cholodkowsky states that Tridactylus, a form allied to Gryllotalpa, bears on the tenth abdominal segment two pairs of cerci (ventral and dorsal), and that the ventral pair may correspond to the atrophied appendages of the tenth embryonic segment of Phyllodromia, with which afterward the eleventh segment becomes fused.

The cercopods are not necessarily confined to the eleventh or to the tenth segment, for when there are only nine segments, with the vestige of a tenth, as in Xiphidium, they arise from the ninth uromere, and in the more modern cockroaches, as Panesthia, in which there are but seven entire segments, they are appended to the last or eighth uromere.

Fig. 184.—Anabrus, ♀, side-view, dissected; showing the relative size of the ovipositor: c, the minute cercopod.—Kingsley del.

As to the homology and continuity of these cercopods with the ventral outgrowths of the embryo, several embryologists, notably Wheeler, are emphatic in regarding them as such. It thus appears that either the embryonic appendages of the seventh or eighth, ninth or tenth uromere may persist, and form the cercopoda of the adult.