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 colony seen from above; B, colony seen 



7 from the side. 



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 



