THE SIMPLEST ANIMALS 



317 



b 



94, 6) . Some of these individuals can take food (by the action 

 of cilia which drive food particles into the mouth, as in a 

 paramecium), and can divide to form new individuals on 

 new branches. Some of the individuals do not feed while 

 attached to the stalk of 

 the colony, but digested 

 food comes to them 

 through the hollow stalk 

 from others which do take 

 and digest food. These 

 specialized non-feed- 

 ing individuals break 

 loose, swim freely for a 

 time, attach themselves 

 to some object, develop 

 a mouth, and soon divide 

 to form two new individ- 

 uals. Then division is 

 repeated again and again 

 and finally results in a 

 new tree-like colony. 



Note that in such a 

 colony there is a slight 

 division of labor in that 



FIG. 94. Vorticella, the bell-animalcule, a, 

 group of seven voiticellas attached to the 

 surface cells of a water-plant. The con- 

 tractile stalk is thrown into a spiral when 

 shortened (see a and c). 6, a single in- 

 dividual ; d, e, division ; /, a free-swim- 

 ming individual formed by division as in 

 d, e. (From Wilson, and Parker.) 



some of the individuals 

 are nutritive, i.e., adapted 

 to feeding and digesting 

 for the benefit of the whole colony ; and others are special- 

 ized for reproducing new colonies. 



Vorticella. These are similar protozoans, the individuals 

 of which live separately. An example is the beautiful bell- 

 animalcule (Vorticella), several of which are shown in Fig. 

 94, a. The food-collecting groove is at the wide end of the 

 bell-shaped body, and a circle of cilia whips particles around 

 the margin and down into a gullet. The stalk contains a cen- 



