x Contents. 



CHAl'TEK PAGE 



XXI. BRANCH ECHINODERMATA 331 



Class I. Asteroidea . . . . . . . . 331 



Class 2. Ophiuroidea . 337 



Class 3. Echinoidea ........ 338 



Class 4. Holothuroidea 343 



Class 5. Crinoidea ........ 345 



XXII. BRANCH PLATYHELMINTHES The Flatworms . . . 348 



BRANCH NEMATHELMINTHES The Roundworms . , . 351 



BRANCH TROCHELMINTHES The Rotifers .... 352 



BRANCH MOLLUSCOIDA 353 



XXIII. CLASSIFICATION OF THE ANIMAL KINGDOM . . . . 355 



INDEX ...... . . . . . . . . 359 



