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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.