74 



BIOLOGY 



Multiplication. Reproduction of Pandorina is of two kinds: 

 1. Each of the cells of the colony divides into sixteen parts, 



which, however, remain 

 attached together, mak- 

 ing a cluster of sixteen 

 groups of sixteen cells 

 each. Then the whole 

 colony breaks up, and 

 each group of sixteen cells 

 forms a new colony liv- 

 ing independently of the 

 others; Fig. 28 B. Thus, 

 by simply dividing, the 

 original colony produces 

 sixteen others. 



2. By the second 

 method of reproduction 

 a conjugation occurs. 

 The cells of a colony 

 break into either sixteen 

 or thirty-two parts, and 

 then the whole mass 

 breaks to pieces, each cell 

 separating, not only from the colony but from its sister cells. 

 Among the hundreds of cells thus formed some are smaller than 

 others; Fig. 28 C and D. After swimming around for a while 

 one of the smaller and one of the larger cells unite with each 

 other; Fig. 28 E and F. The combined mass then secretes a red 

 shell or cyst about itself and remains dormant for a time, show- 

 ing no signs of motility, H. Later, however, it resumes its 

 activity and may divide into two or three parts, which then 

 escape from the cyst and swim around for a time as single cells, 

 called swarm spores, /. Eventually each divides into sixteen 

 cells which remain together, forming a new colony like the, 

 original, J 



H 



FIG. 28. PANDORINA, A COMMON FRESH- 

 WATER, COLONIAL, UNICELLULAR ANIMAL 



A, the animal in its adult condition. 



B, showing the method of reproduction by simple 

 division, each cell dividing into sixteen parts and 

 the whole colony breaking up into sixteen colonies. 



C to J shows the successive stages of reproduction 

 accompanied by conjugation ; C, the larger of the unit- 

 ing cells; D, the smaller ones;E, their conjugation; 

 //, the dormant condition within the cyst. For de- 

 scription, see text. 



