SECTION II. 

 INVERTEBRATES. 



CHAPTER VII. 



Arthropoda. 



WE have so far completed our survey of most of the British Vertebrates, from 

 Mammals to Fishes, and we next proceed to the Invertebrates that is, to the 

 animals that do not possess backbones. These are divided into thirteen 

 groups, of which the following are important for students of British Nature. 



1. Arthropoda ("Jointed-limbed ") a group which includes Crabs, Lobsters, 

 Shrimps, Wood-lice, Spiders, Insects, etc. 



2. Mollusca Shellfish, including Cuttle-fish, Snails, Whelks, Oysters, etc. 



3. Echinodermata (" Spiny-skinned "), in which are placed Sea-urchins, 

 Starfish, etc. 



4. Polyzoa, or Moss Animals, such as Corallines, Sea-mats, etc. 



5. Annelida, or Worms, such as Earthworms, Sea-mice, etc. 



6. Platyhelminthes, or Flatworms. 



7. Ccelenterata (Zoophytes), to which belong Sea-anemones, Corals, and 

 Jelly-fishes. 



8. Porifera Sponges. 



9. Protozoa, or Animalcula. 



The first group ARTHROPODA contains as its first class the Crustacea 

 (Crabs, Lobsters, Crayfish, Shrimps, etc.). Most of the Crustacea are aquatic, 

 living either in salt or fresh water, or in damp places. Their bodies are com- 

 posed of a number of ring-like segments jointed together, each segment having 

 a pair of limbs. They have no inner skeleton, the flesh being supported and 

 protected by a " crust " (hence the name Crustacea, from the Latin, crusta, 

 which in common parlance is a shell] as, for instance, that of the Crab. They 

 breathe by means of gills. They shed their shells periodically ; and if they 

 lose a limb, they can grow a new one to take its place. 



Most of the Crustaceans lay eggs, and the young when hatched pass through 

 various stages until they reach their mature or adult form. Many of them 

 feed on dead creatures or decaying organic matter, a few being herbivorous. 



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