The intestine opens into the apex of the tail, and is surrounded by a liver.
The sexual parts still open for the most part on the thorax, and indeed by two orifices, as in the Worms.
There are no more androgynous or bisexual beings in the present class.
In some few the branchiæ already enter the body and become air-tubes, as in the Scolopendræ, Spiders and Scorpions.
The Branchial animals repeat, as being the second class of their circle, the Corals and Snails; their "quasi" coat of mail is therefore harder, often richer in calcareous ingredients, and, in addition to this, lies frequently upon the thorax or branchia as a special testa, called the scute or shield.
Class 9. Tracheal, Alary Animals.
Annulate animals, whose branchiæ have undergone a partial conversion into tracheæ and into wings, are the Insecta proper or Flies.
3263. A Worm with feet, tracheæ and wings, is an Entomon or Insect.
3264. The first separation takes place in respect to the three tegumental segments of the body, the abdomen, thorax, and head. All three are, in the Insects, more separated from each other than in the Branchial animals, and united together usually by a narrow tube; even in cases also, where they are connate with each other, they are still easily recognized by respect being had to size, form, or appendages.
Every Insect is divided into three segments. In the abdomen are the organs belonging to the Worm, such as the intestine, and a fatty body which appears to be an analogue of the liver, a dorsal vessel, tubular sexual parts and air-tubes (tracheæ), but nothing else.