284 ARTICULATA: INSECTA. 



divided. The number of these nervous centers is gener- 

 ally the same as the number of the segments (somites) of 

 the body. 



The Branch of Articulata is the equivalent of the Sub- 

 Kingdoms of Arthropoda and Vermes recognized by some 

 authors.* It is also about the same as the Annulosa of 

 Huxley. The Articulate plan is carried out in three dif- 

 ferent ways, giving three Classes : 



I. INSECTA or Insecteans, or articulate animals whose respiration 



is agrial; their respiratory apparatus consists of a system of 

 air-tubes or tracheae in some cases, as in Spiders, of lung-like 

 cavities which receive air through air-holes or stigmata on 

 the sides, or posterior part of the body ; as Bees, Butterflies, 

 Flies, Beetles, Bugs, Grasshoppers, Spiders, Centipedes, etc. 



II. CRUSTACEA or Crustaceans, or articulates which are aquatic 



in their mode of respiration ; their respiratory apparatus con- 

 sists of gills or branchiae. These articulates are covered with 

 a hardened skin or crust ; as Crabs, Lobsters, Shrimps, Sand- 

 fleas, Barnacles, etc. 



III. VERMES or Worms, or the simplest forms of articulates, or 



those made up of many similar segments, with no division 

 into regions such as are seen in Insecteans and Crustaceans, 

 but like the latter effecting respiration by means of gills or 

 gill-like organs, and living in water or in moist places. 



* Gegenbaur, Rolleston, and some others, recognize seven Branches or 

 Sub-Kingdoms, thus : 



Sub-Kingdoms 1. VERTEBRATA. 2. MOLLTJSCA. 3. ARTHROPODA. 

 4. VERMES. 5. ECHINODERMATA. 6. COELENTERATA. 7. PROTOZOA. 



ARTHROPODA (Insects, Spiders, Myriapods, and Crustaceans), and VERMES 

 (Worms proper and their allies), in this classification, are equivalent to the 

 old Branch Articulata. And the ECHINODERMATA (Sea-cucumbers, Sea- 

 urchins, Star-fishes, and Crinoids), and COJLENTERATA (Jelly-fishes proper, 

 Polyps, and Hydroids), are equivalent to the old Branch Radiata. 



The word Vertebrata comes from the Latin verto, to turn ; Articulata, from 

 the Latin articulus, diminutive of artus, a joint ; Mollusca, from the Latin 

 mollis, soft ; Radiata, from the Latin radius, a ray or spoke ; Arthropoda, 

 from the Greek artkron, a joint, and p&us, a foot ; Vermes, from verto, to 

 turn ; Echinodermata, from the Gr. ecfdnos, a hedgehog, and derma, skin ; 

 Coelenterata, from the Gr. koilos, hollow, and entera, viscera ; and Protozoa, 

 from the Gr. protos, first, simplest, and f.oim, animal. 



