ARTHROPODA. 81 



Phylum III. ARTHROPODA. 



The heteronomously segmented body with jointed lateral appendages, 

 brain and ventral ganglionated chain, and chitinous exoskeleton. 

 Vascular system, when present, not closed, but communicates with the 

 irregular spaces which make up the body-cavity. Enterocoelic spaces 

 inconspicuous. Sexes almost always distinct. Development frequently 

 with metamorphosis ; sometimes parthenogenesis. 



See note, p. 62. 



