Class IV. INFUSORIA, Ledermüller, 1763 198 Genus. _Balantidium_, Claparède et Lachmann 200 _Balantidium coli_, Malmsten, 1857 200 _Balantidium minutum_, Schaudinn, 1899 204 Genus. _Nyctotherus_, Leidy, 1849 204 _Nyctotherus faba_, Schaudinn, 1899 205 _Nyctotherus giganteus_, P. Krause, 1906 205 _[Nyctotherus] africanus_, Castellani, 1905 206 THE CHLAMYDOZOA 207 PROTOZOA INCERTÆ SEDIS 210 _Sergentella hominis_, Brumpt, 1910 210 *B. Platyhelminthes (or Flat Worms)* 211 CLASSIFICATION OF THE PLATYHELMINTHES. Class I. TURBELLARIA (or Eddy Worms) 212 Order 1. _Rhabdocœlida_ 212 2. _Tricladida_ 212 3. _Polycladida_ 212 Class II. TREMATODA (Sucking Worms) 212 III. CESTODA (Tapeworms) 212 Class II. TREMATODA, Rud. 212 Development of the Trematodes 222 Biology 229 CLASSIFICATION OF THE TREMATODES OF MAN.