EUPHYCOPHYTA 25 



colony or to an akinete, or they will divide and pass into a tempor- 

 ary palmelloid state before becoming motile once more. Sexual 

 reproduction is by means of naked isogametes, fusion occurring 

 between gametes derived from separate colonies which must there- 

 fore represent +■ and - strains. The resulting quadriflagellate 



Fig. 4 Gonium pectorale. A-D, stages in the formation of a 

 coenobium. E, colony ( x 520). F, zygote. G, H, stages in germina- 

 tion of zygote. J, four-celled colony. (A-D, after Fritschj E, after 



Smith; G-J, after Kniep.) 



zygote soon comes to rest and subsequently germinates, when it 

 gives rise to four biflagellate haploid cells which are liberated to- 

 gether as a small colony. When the later development of these cells 

 is followed it is found that two of them give rise to + and two to - 

 colonies, suggesting that meiosis must take place at germination of 

 the zygote. 



Volvocaceae: Pandorina (after Pandora's box). Fig. 5 



In this genus typical chlamydomonad cells are aggregated to- 

 gether to form oblong or spherical colonies. The number of cells 

 in a colony ranges from four to eight, sixteen or thirty-two, sixteen 



