These remarkable hyper-metamorphoses remind us of the metamorphosis of the embryo of Echinoderms into the Pluteus-and Bipinnaria-forms of the starfish, sea urchins and Holothurians;[24] of the Actinotrocha-form larva of the Sipunculoid worms; of the Tornaria into Balanoglossus, the worm; of the Cercaria-form larva of Distoma; of the Pilidium-form larva of Nemertes; and the larval forms of the leeches;[25] as well as the mite Pentastomum, and certain other aberrant mites, such as Myobia. While Fritz Mueller and Dohrn have considered the insects as having descended from the Crustacea (some primitive zoea-form), and Dohrn has adduced the supposed zoea-form larva of these egg-parasites as a proof, we cannot but think, in a subject so purely speculative as the ancestry of animals, that the facts brought out by Ganin tend to confirm our theory, that the ancestry of all the insects (including the Arachnids and Myriopods) should be traced directly to the worms. The development of the degraded, aberrant Arachnidan Pentastomum accords, in some important respects, with that of the intestinal worms. The Leptus-form larva of Julus, with its strange embryological development, in some respects so like that of some worms, points in that direction, as certainly as does the embryological development of the egg-parasite Ophioneurus. The Nauplius form of the embryo or larva of nearly all Crustacea, also points back to the worms as their ancestors, the divergence having perhaps originated, as we have suggested, in the Rotatoria. While the Crustacea may have resulted from a series of prototypes leading up from the Rotifers (Fig. 198), it is barely possible that one of these creatures may have given rise to a form resulting in two series of beings, one leading to the Leptus form, the other to the Nauplius. For the true Annelides (Chaetopods) are too circumscribed and homogeneous a group to allow us to look to them for the ancestral forms of insects. But that the insects may have descended from some low worms is not improbable when we reflect that the Syllis and allied genera of Annelides bear appendages consisting of numerous joints; indeed, the strange Dujardinia rotifers, figured by Quatrefages, in its general form is remarkably like the larva of Chloeon. It has a quite distinct head, bearing five long, slender, jointed antennae, and but eight or nine rings to the body, which ends in two long, many jointed appendages exactly like the tentacles. Quatrefages adds, that its movements are usually slow, but "when it wishes to move more rapidly, it moves its body alternately up and down with much vivacity, and shoots forwards by bounds, so to speak, a little after the manner of the larvae of the mosquito" (Histoire Naturelle des Anneles, Tome 2, p. 69). The gills of aquatic insects only differ from those of worms in possessing tracheae, though the gills of the Crustacea may be directly compared with those of insects. [Illustration: 198. A Rotifer.]