390 SYNOPSIS 



VI. BRIEF DESCRIPTIONS OF TYPES OF THE HIGHER GROUPS OF 

 ANIMALS AND PLANTS IN TERMS OF POLYGORDIUS AND OF 

 THE FERN RESPECTIVELY. 



PAGE 



a. Animals. 



All are triploblastic and ccelomate. " 



35. Starfish. 



Radially symmetrical : discontinuous dermal exoskele- 

 ton : characteristic organs of locomotion (tube feet) in 

 connection with ambulacral system of vessels 309 



36. Crayfish. 



Metamerically segmented : segmented lateral append- 

 ages : differentiation of metameres and appendages : 

 continuous cuticular exoskeleton discontinuously calci- 

 fied : gills as paired lateral offshoots of the body-wall : 

 heart as muscular dilatation of dorsal vessel : ccelome 

 greatly reduced and its place taken by an extensive series 

 of blood-spaces : nervous system sunk in the mesoderm 

 and consisting of brain and ventral nerve-cord 314 



37. Mussel. 



Non-segmented : mantle formed as paired lateral out- 

 growths of dorsal region : foot as unpaired median out- 

 growth of ventral region : cuticular exoskeleton in the 

 form of a calcified bivalved shell : gills as paired lateral 

 outgrowth of body-wall : heart as muscular dilatation of 

 dorsal vessel : ccelome reduced to pericardium : nervous 

 system consists of three pairs of ganglia sunk in the 

 mesoderm 320 



38. Dogfish. 



Metamerically segmented : differentiated into head, trunk, 

 and tail : trunk alone ccelomate in adult : appendages as 

 median (dorsal, ventral, and caudal) and paired (pectoral 

 and pelvic) fins : discontinuous dermal exoskeleton and 

 extensive endoskeleton of partially calcified cartilage, 

 including a chain of vertebral centra below the nervous 

 system replacing an embryonic notochord : gills as 

 pouches of pharynx opening on exterior : heart as 

 muscular dilatation of ventral vessel : hollow dorsal 

 nervous system not perforated by enteric canal 324 



/>. Hants. 



All exhibit alternation of generations and the series 

 shows the gradual subordination of the gamobium to the 

 agamobium. 



