The Planariæ are slightly different from the Liver-flukes or Fasciolæ hepaticæ, since they are white, bloodless, have a ramified intestine without anus, and increase also by fissiparous generation. They belong to the present order, although they live not as parasites, but in a state of freedom.
Fam. 2. Rhizopodoid Worms, Hydatids.
Body annulate or articulate, with a claviform proboscis without an intestine; they appear to have several mouths.
The Cystica develop ova simply upon the internal wall of the tegument; the body's last ring is expanded into a cystic form, and is mostly much larger than the whole body. The Cœnurus cerebralis, or Brain-hydatid, ramifies like the Polyps.
The Cestoidea have in each joint or member of the body an ovarium, and, as it would appear, male parts also, so that they are androgynous. The sexual orifices are at the border or upon the surface of the posterior members. The member can be viewed as an ovarium liberating itself; as in the Lerneæ and Arguli.
The Filariæ or Thread-worms, which also belong here, are in the form of a cylindrical tube, with separate sexual parts, which open posteriorly.
Fam. 3. Rotiferal Worms, Ascarides.
Body cylindrical, intestine free, with mouth and anus; sexual parts separate.
Upon the mouth these Entozoa have some papillæ or points, which may be regarded as tentacula. The larger species have a distinct nervous cord. The Gordius cannot well take any other position than the present, although it does live in a state of freedom.
Order 2. Polypary Worms—Hirudines.