The internal reproductive system in the 6th male larval instar of D. punctatus consists of a pair of testes, vasa deferens and the genitial cavity (Herold’s organ). Two kidney-shaped testes occur laterally just under each side of the heart in the 5th abdominal segment. From the concave middle of each testis, the vas deferens extends into the 9th segment and connects with the genitial cavity, which is a pear-shaped constructure lying on the middle of the ventral posterior margin of the 9th segment.The internal reproductive system of the 6th femae larval instar of D. punctatus comprises paired ovaries, lateral oviducts and two pairs of imaginal disks. Paired ovaries occur in the 5th abdominal segment. Their positions are similar to those of the testes of the male larvae. From the posterior ends of the ovaries the lateral oviducts pass the 6th segment and terminate on the ventral posterior margin of the 7th segment. In the 4th female larval instar two pairs of imaginal disks begin to appear in the 8th and 9th segments.Externally the concaveness of the genital cavity starts to appear in the 3rd male instar larvae while the external marks of the imaginal disks on the 8th and 9th abdomjnal segments can be recognized in the 4th female larval instar.On the basis of the morphology of the reproductive system, the methods to sex the larvae of D. punctatus are discussed,