CHAPTER XII 







BACKBONELESS ANIMALS 



1. Protozoa 2. Sponges 3. Stinging-animals or Coelentera 4. 

 " Worms " 5. Echinoderms 6. Arthropods 7. Molluscs 

 8. Other Types 



1. Protozoa. It is likely that the first breath of life was 

 in the water, for there most of the simplest animals and 

 plants have their haunts. We call them simple, but 

 there was much truth in Ehrenberg's view, who described 

 some of them in 1838 as " perfect organisms." He was 

 wrong in thinking he saw stomach, heart, and similar 

 organs in them, but right in recognising that they often 

 have a very intricate structure. 



There is a widespread erroneous idea that these animal- 

 cules are to be found swarming in any drop of water. 

 The clear water of daily use will generally disappoint, or 

 rather please us by showing little trace of living things. 

 But take a test-tube of water from a stagnant pool, hold 

 it between your eyes and the light, and it is likely that 

 you will see many forms of life. Simple plants and 

 simple animals are there, the former represented by 

 threads, ovals, and spheres in green, the latter by more 

 mobile almost colourless specks or whitish motes which 

 dance in the water. But besides these there are jerky 

 swimmers whose appearance almost suggests their popular 

 name of " water-fleas," and wriggling " worms," thinner 

 than thread and lither than eels : both of these may be 

 very small, but closer examination shows that they have 

 parts and organs, that they are many-celled not single - 

 celled animals. 



Vary the observations by taking water in which hay 



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