In regard to the sexual openings of worms, though their position is in general in the anterior part of the body, it is still very variable, though, in general, paired. In the oligochete worms the genital zone, with the external openings, is formed by the segments lying between the 9th and 14th rings, though in some the genital organs are situated still nearer the head. The myriopods, which evolved from the worms earlier than insects, appear to have in their most primitive forms (the Diplopoda) retained this vermian position of the genital outlets. In the later forms, the chilopods, the genital openings have been carried back to near the end of the body, as in insects. From observations made by three different observers on the freshly hatched larva of the Julidæ, it appears that the ancestral diplopods were six-footed, or oligopod, the larva of Pauropus (Fig. 13) approaching nearest to our idea of the ancestral myriopod, which might provisionally be named Protopauropus. =Relations of the Symphyla to Insects.=—Opinions respecting the position of the Symphyla, represented by Scolopendrella (Fig. 14), are very discordant. By most writers since Newport, Scolopendrella has been placed among the myriopods. The first author, however, to examine its internal anatomy was Menge (1851), who discovered among other structures (tracheæ, etc.) the silk-glands situated in the last two segments, and which open at the end of each cercus. He regarded the form as “the type of a genus or family intermediate between the hexapod Lepismidæ and the Scolopendridæ.” [Illustration: FIG. 13.—_Pauropus huxleyi_, much enlarged. _A_, enlarged view of head, antennæ, and first pair of legs (original). _B_, young.—After Lubbock. _C_, longitudinal section of _Pauropus huxleyi_, ♂: _a_, brain; _b_, salivary gland; _k_, mid-intestine; _g_, rectum; _h_, ventral nerve-cord; _c_, bud-like remnants of coxæ; _d_, penis; _e_, vesicula seminalis; _f_, ductus glandularis; _i_^1, divisions of testes.—After Kenyon. ] In 1873[5] the writer referred to this form as follows: “It may be regarded as a connecting link between the Thysanura and Myriopoda, and shows the intimate relation of the myriopods and the hexapods, perhaps not sufficiently appreciated by many zoölogists.” In 1880 Ryder regarded it as “the last survival of the form from which insects may be supposed to have descended,” and referred it to “the new ordinal group Symphyla, in reference to the singular combination of myriopodous, insectean, and thysanurous characters which it presents.[6]” [Illustration: