CHAPTEE V 



The first division of the Arthropoda — The organisation and development 

 of the Crustacea. 



THE FIFTH RACE OR PHYLUM OF THE ANIMAL KINGDOM. 



ARTHROPODA— ARTICULATA. 



Bilaterally symmetrical animals with chitinous exoskeleton, seg- 

 mented body, and paired jointed extremities on all or some of the 

 segments. With brain, oesophageal commissures, and segmented ventral 

 chord. With heart lying above the intestine. Sexes separate, with 

 one pair of sexual glands and originally paired ducts from these glands. 



Fipst Sub-race or Sub-phylum. 



Branehiata. — Aquatic animals. With the exception of the anterior 

 antenna all the appendages are morphologically biramose. Resiji- 

 ration cutaneous or by means of gills, which are almost always 

 appendages of the basal joints of the limbs. 



Single Cl.vss. Crustacea. 



First a-ppendage to the Sub-race Branehiata : The Trilobites, Gigantostraca, 

 Hemiaspidse, and Xiphosura. 



Second appendage to the Sub-race Branehiata : The Pantopoda or Pycno- 

 gonidse. 



Second Sub-race or Sub-phylum. 



Tracheata. — Land animals. Limbs not biramose,' consisting of a 

 single row of joints. Respiration by means of tracheae (tubular 

 or book-leaf tracheae). 



Cla.ss I. Protracheata. 



Class IL Antennata (Myriapoda and Hexapoda). 



Class III. Chelicerota sive Arachnoidea. 



Appendage to the Phylum of the Arthropoda. 

 The Tardigrada or Bear animalcules. 



