THE LIFE OF THE SLIGHTLY COMPLEX ANIMALS 25 



there is formed a group of a few or many cells, each cell 

 having the structure of the simpler unicellular forms. 

 These cells are held together in a gelatinous envelope, and 

 the mass is usually spherical in shape. In most of the 

 colonies each of the cells possesses two or three long, pro- 

 toplasmic, whiplash-like hairs, called flagella, and by the 

 lashing -of these flagella in the water the whole group swims 

 about. 



14. Gonium. If, when one of the simplest animals di- 

 vided to form two daughter cells, these two cells did not 

 move apart, but remained 

 side by side and each di- 

 vided to form two more, 

 and each of these divided 

 to form two more, and 

 these eight divided each 

 into two, each cell com- 

 plete and independent but 

 all remaining together 

 in a group if this pro- 

 cess should take place we 

 should have produced a 

 group or colony of sixteen 

 cells, each cell a complete 

 animal capable of living 

 independently like the 

 other simplest animals, 

 but all holding together B 



to form a tiny, flat, plate- FIG. 12. Gonium pectorale (after STEIN). A, 



like colony. Now, this is *j^^^ ab ve; B ' C lony 8een 

 precisely what takes place 



in the case of those colonial Protozoa belonging to the genus 

 Gonium (Fig. 12). When the mother cell of Gonium di- 

 vides, the daughter cells do not swim apart, but remain 

 side by side, and by repeated fission, until there are sixteen 

 cells side by side, the colony is formed. Each cell of the 



