CHAPTER VI. 



AETHROPODA. 



Animals more or less resembling in structure the 

 Lobster (type of the water-breathing Arthropoids), 

 or the Cockroach (type of the air-breathing Arthro- 

 poids). 



Classes. — Cktistacea, or Lobster-like animals. 



Sub-classes : Entomostkaca and Malacostkaca. 



\ C3 



Arachnida, or Spider-like animals. 

 Pkototracheata ; Peripatus. 

 Mteiopoda, or Millipedes. 

 Hexapoda, or true Insects. 



These are bilateral segmented animals, with legs and 

 segments which are modified for various purposes. 

 The most apparent general characteristic is the pre- 

 sence in the adult of a hard, shell-like exoskeleton. 

 There is a highly developed nervous system ; and the 

 higher forms are exceedingly highly organized and 

 possessed of a great deal of intelligence. They 

 receive their name (joint-footed) from their legs, 

 which are necessarily attached by joints, because the 

 animal is covered with a hard " shell." 



The Ceitstacea nearly all live in water, and breathe, 

 where distinct breathing organs are developed, by gills. 



The Entomosteaca (or Crustacea with divided shells) 

 are mostly fresh-water forms. They include the so- 

 called water fleas. They make excellent microscopic 



