CHLAMYDOMONAS, SEXUAL REPRODUCTION 185 



body (Fig. 97, e, /), known as a zygospore, sinks to the bottom 

 and enters upon a resting condition. 



The process of reproduction just described is known as a 

 sexual one since, as in all such processes, the fusing together 

 of two distinct individuals is involved. Despite the fact that 

 the gametes are outwardly all alike, there is evidently some 

 internal (probably chemical) difference between them, for it 



FIG. 97. Sexual reproduction of Chlamydomonas. a, two gametes of 

 C. pertyi ; b and c, stages in the fusion of the same ; d, zygote, and e, 

 zygospore of C. pertyi ; /, zygospore of C. reinhardii ; g, microgamete, 

 and h, macrogarhete of C. monadina ; i-k, stages in fusion of gametes 

 of the same, ma., nucleus of macrogamete ; mi., ditto of microgamete ; 

 n., fusion-nucleus (in k) ; p., pyrenoid. (All after Goroschankin.) 



has occasionally been observed that only gametes derived from 

 distinct parent-individuals are attracted towards one another 

 and fuse together. In one species of Chlamydomonas (C. mona- 

 dina) , however, sexual union always takes place between gametes 

 which differ both in size and behaviour. Some, produced by 

 few divisions of an individual, are large (macrogametes, Fig. 97, h), 

 relatively sluggish in their movements, and soon come to rest 

 (although the cilia persist), whilst others, formed by numerous 



