82 DIVERSIONS OF A NATURALIST 



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another and differ from the vast majority of animals, • 

 such as worms, sea-urchins, star-fishes, whelks, mussels, 

 crustaceans, insects, spiders and vertebrates (which last 

 include fish, reptiles, birds, and mammals"). These all 

 have a second chamber, or body cavity, quite shut off 

 from the digestive cavity and from the direct access of 

 water and food particles. This second distinct chamber 

 is filled with an animal fluid, the lymph, and is called 

 the " Coelom" (a Greek word meaning a cavity). These 

 higher animals, which possess a coelom as well as a gut, 

 or digestive cavity, are called " Ccelomata," or " Coelo- 

 mocoela," in consequence ; whilst the sea-anemones, 

 polyps, and jelly-fish form a lower grade of animals 

 devoid of coelom, but having the one cavity, or gut, 

 continued into all parts of the body. Hence they are 

 called " Coelentera," or " Enterocoela," words which mean 

 that the cavity of their bodies (Greek cce/) is made by 

 an extension of the gut, or digestive cavity (Greek 

 enteron). The higher grade of animals — the Coelo- 

 mocoela — very usually have a vascular system, or 

 blood-vessels and blood, as well as a coelom and lymph, 

 and quite independent of it ; also some kind of kidneys, 

 or renal excretory tubes. Neither of these are possessed 

 by the sea-anemones and their allies — the Enterocoela — 

 but they have, like higher animals, a nervous system and 

 also large ovaries and spermaries on the walls of their 

 single body cavity, which produce their reproductive 

 germs. These pass to the exterior, usually through the 

 mouth, but sometimes by rupture of the body wall. 



All " one-cavity " animals, the Enterocoela or Coelen- 

 tera, produce peculiar coiled-up threads in their skin in 

 great quantity — many thousands — often upon special 

 warts or knobs. These coiled-up threads lie each in a 

 microscopic sac ; they are very delicate and minute 



