482 SYNOPSIS 



VI. BRIEF DESCRIPTIONS OF EXAMPLES OF THE HIGHER GROUPS 

 OF ANIMALS AND PLANTS. 



a. ANIMALS. 



All are triploblastic and coelomate. 



34. Starfish. 



Radially symmetrical : discontinuous dermal exoskele- 

 ton : characteristic organs of locomotion (tube feet) in 

 connection with ambulacral system of vessels 306 



35. 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 dilation of do sal vessel : ccelome 

 greatly reduced and its place taken by an extensive series 

 of blood-spaces : nervous system sunk in the mesoderni 

 and consisting of brain and ventral nerve-cord 318 



36. 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 

 outgrowths of body-wall : heart as muscular dilatation of 

 dorsal vessel : coelome reduced to pericardium : nervous 

 system consists of three pairs of ganglia sunk in the 

 mesoderm 348 



37. Dogfish. 



Metamerically segmented : differentiated into head, trunk, 

 and tail : trunk alone coelomate 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 366 



b. PLANTS. 



All exhibit alternation of generations and the series 

 shows the gradual subordination of the gamobium to the 

 agamobium. 



