161, _lc_; 162, the same enlarged), in Tomocerus consists of two bundles of spinules, one broad like a ruffle, and the other slender, pencil-like, ending in an inner row of spines, like the spinules on the lacinia of the Japyx and Campodea and, more remotely, the laciniae of the three sub-orders of insects above referred to. There is also a horny, prominent, three-toothed portion (Fig. 161, _g_). These homologies have never been made before, so far as the writer is aware, but they seem natural, and suggested by a careful examination and comparison with the above-mentioned mandibulate insects. [Illustration: 159. 161. 160. 162. Tomocerus plumbeus and mouth-parts, greatly enlarged.] The spring consists of a pair of three-jointed appendages, with the basal joints soldered together early in embryonic life, while the other two joints are free, forming a fork. It is longest in Smynthurus and Degeeria, and shortest in Achorutes (Fig. 172, _b_), where it forms a simple, forked tubercle; and is obsolete in Lipura and Anura, its place being indicated by an oval scar. The third joint varies in form, being hairy, serrate and knife-like in form, as in Tomocerus (Fig. 159, _a_), or minute, with a supplementary tooth, as in Achorutes (Fig. 172, _c_). This spring is in part homologous with the ovipositor of the higher insects, which originally consists of three pairs of tubercles, each pair arising apparently from the seventh, eighth, and ninth (the latter the penultimate) segments of the abdomen in the Hymenoptera. The spring of the Podura seems to be the homologue of the third pair of these tubercles, and is inserted on the penultimate segment. This comparison I have been able to make from a study of the embryology of Isotoma. [Illustration: 163. Catch holding spring of Achorutes.]