ii8 FIRST LFSSONS IN ZOOLOGY 



leaf or stem or root in the water of a stagnant pool. 

 Touch such a spot -vvith a needle, and if it is a bell- 

 animalcule colony it will contract instantly. Bring sev- 

 eral colonies into the schoolroom and keep in a glass of 

 stagnant water. Examine a colony in a drop of water 

 in a -watch-glass or on a slide under the microscope. 

 Note the stemmed bell-shaped bodies which compose it. 

 Ivich bell and stem together form an individual. Tap 

 the slide and note the sudden contraction of the colony. 

 Observe the contraction of a single individual. Just what 

 takes place.' Watch an individual expand. Examine 

 carefully the "bell." Its upper margin is fringed with 

 cilia, and there is a mouth opening on the upper surface. 

 Eind a contractile vacuole in the body, and also numer- 

 ous food particles which move about. The nucleus, hard 

 to see, is elongate and curved. The body is inclosed by 

 a thin cuticle. Make a drawing of a Vorticella expanded, 

 and of one contracted. 



Both ParanKecium and Vorticella multiply by division; 

 that is, by the simple dividing of the body in two, as with 

 Amceba. But each of these halves, or new animals, is 

 not exactly like its parent, and has to undergo some 

 change or development as well as growth (increase in 

 sizej to become a complete Paramcecium or Vorticella. 

 These two kinds of one-celled animals, and most others, 

 also have another process of multiplication slightly more 

 complex than the one just described. Two individuals 

 sometimes come together and a part of the nucleus of 

 each passes into the body and fuses with the remaining 

 part of the nucleus of the other. Then the individuals 

 move apart, and each divides in halves. This process 

 is called multi[)lication b)' conjugation .and division. Per- 

 ]ia])s AmcL'b:e conjugate occasionall)', but if so the}- do it 

 rarely. On the other hand ParanKecium and Vorticella 

 cannot go (;n indefinitely having generations by simple 



