26 



ANIMAL LIFE 



colony eats and breathes and feels for itself ; each can and 

 does perform all the processes necessary to keep it alive. 

 When ready to multiply, the sixteen cells of the Gonium 

 colony separate, and each cell becomes the ancestor of a 

 new colony. 



15. Pandorina. Another colony usually composed of six- 

 teen cells is Pandorina, but the cells are arranged to form 

 a spherical instead of a plate-like colony (Fig. 13). In Pan- 

 dorina morum the colony consists of sixteen ovoid cells in 

 a spherical jelly-like mass. Each cell has two flagella, and 

 by the lashing of all the flagella the whole colony moves 

 through the water. Food is taken by any of the cells, is 

 assimilated, and the cells increase in size. When Pan- 

 dorina is ready to multiply, each cell divides repeatedly 

 until it has formed sixteen daughter cells. The inclosing 

 gelatinous mass which holds the colony together dissolves, 



and the daughter colonies be- 

 come free and swim apart. 

 Each colony soon grows to the 

 size of the original colony. 

 This kind of multiplication or 

 reproduction may be continued 

 for several generations. But 

 it does not go on indefinitely. 

 After a number of these gener- 

 ations has been produced by 

 simple division, the cells of a 

 colony divide each into eight 

 instead of sixteen daughter 

 cells. The daughter cells are 

 not all of the same size, but 

 the difference is hardly notice- 

 able. The eight cells resulting from the repeated division 

 of one of the original cells separate and swim about inde- 

 pendently by means of their flagella. If one of these cells 

 comes near a similar free-swimming cell from another 



PIG. 13. Pandorina sp. (from Na- 

 ture). The cells composing the 

 colony are beginning to divide to 

 form daughter colonies. 



