xiv CONTENTS 



GROUP III. ENTOMOSTRACA (LOWER CRUSTACEA). 



PAGE 



ORDER V.: OAR-LEGGED CRUSTACEA ... ... ... ... 424 



VI.: BIVALVED CRUSTACEA ... ... ... ... .. 424 



,, VII.: LEAF-LEGGED CRUSTACEA ... ... ... ... 425 



VIII. : BARNACLES ... ... ... ... ... ... 425 



III. BODY SOFT, WITHOUT JOINTED LIMBS ; WITH A VENTRAL ORGAN 

 OF LOCOMOTION (FOOT); A FOLD OF SKIN (MANTLE) ABOVE THE 

 FOOT, WHICH PROTECTS THE EESPIRATORY ORGANS, AND USUALLY 

 EXCRETES A CALCAREOUS SHELL. 



III. Phylum : Mollusca 427 



(a) ASYMMETRICAL MOLLUSCA WITH HEAD, FLAT-SOLED FOOT, AND USUALLY 



SPIRAL SHELL. 



CLASS I.: GASTROPODS ... ... ... ... ... ... ... 428 



ORDER I. : AIR-BREATHING GASTROPODS ... ... ... ... 428 



II.: GILL-BREATHING GASTROPODS ... ... ... ... 434 



III.: WINGED GASTROPODS ... ... ... ... ... 434 



(6) SYMMETRICAL MOLLUSCS WITHOUT DISTINCT HEAD, WITH WEDGE- 

 SHAPED FOOT, AND WITH BIVALVE SHELL. 

 CLASS II.: BIVALVES ... ... .... ... ... ... ... 435 



(c) SYMMETRICAL MOLLUSCS WITH DISTINCT HEAD, WITH FOOT DEVELOPED 



INTO ARMS SURROUNDING THE MOUTH, AND POSTERIOR FUNNEL. 



CLASS III.: CUTTLE-FISHES ... ... ... ... ... ... 442 



IV. WITHOUT SEGMENTED LIMBS; BODY ENCLOSED BY A DERMO- 

 MUSCULAR TUBE. 



IV. Phylum : Vermes ... ... ... .,. ... ... ... 446 



(a) BODY CONSISTING OF NUMEROUS SIMILAR SEGMENTS. 



CLASS I.: SEGMENTED WORMS ... ... ... ... ... ... 446 



ORDER!.: BRISTLE-WORMS ... ._.. ... ... ... 446 



,, II.: LEECHES ... ... ... ... ... ... 451 



(&) BODY CYLINDRICAL, NOT SEGMENTED. 

 CLASS II.: THREAD- WORMS ... ... ... ... ... ... 452 



(c) BODY FLAT. 



CLASS IIL: FLAT-WORMS ... ... ... ... ... ... 454 



ORDER I. : TAPE-WORMS ... ... ... ... :,,.. ... 454 



II.: FLUKES 458 



