Threadworm (Nematodes) or Roundworm is composed of many different species. In all the body is slender as in the "vinegar eel". This small worm, a millimeter or two in length, lives on the various forms of mold that grow in fermenting fruit juices. A tough cuticle surrounds the body, perserving its shape and at the same time protecting the delicate organs against the action of the acids in which it lives. In the treadworm the eggs develop within the body and the young are born with the form of the parent.