670 SEXUALITY 



but the clones are divisible into two physiological types, with copula- 

 tion taking place only between the two types of clones. Under these 

 conditions, the type of each clone is identical with the type of its left- 

 over cells under normal conditions. 



These results of Moewus show that different clones of C. eugametos 

 f. subheteroica produce different kinds of gametes and that in mixtures 

 of left-over cells and in mixtures of chemically treated cultures copula- 

 tion is between physiologically diverse types of gametes. His further 

 conclusion that the copulation occurring under normal conditions within 

 each clone is also between the same two types of gametes has not been 

 directly demonstrated, though it appears a reasonable inference. The 

 possibility that copulation is here taking place between gametes of the 

 same type has not been excluded. Convincing evidence on this important 

 question calls for direct tests with "split pairs," as performed by Kimball 

 (1939a) on Payanieciuni (see p. 697). 



The other two races showing copulation within a clone, C. eugametos 

 f. synoica and C. dresdensis, differ from C. eugametos f. subheteroica in 

 three respects : ( 1 ) copulation occurs presumably on a much larger scale 

 within a clone, the proportion of left overs being relatively small; (2) 

 in different cultures of the same clone the left overs may be of different 

 types; (3) no environmental means of suppressing or decreasing copula- 

 tion within the clone has been reported. Otherwise the observations re- 

 ported for these two races agree with those reported for C. eugametos 

 f. subheteroica. Mixture of the left overs from different cultures in all 

 possible combinations of two shows that in each race there are two kinds 

 of left-over gametes, with copulation occurring only between the two 

 kinds. The same uncertainty attaches here to Moewus's conclusion that 

 the copulations within a clone are likewise between gametes of different 

 type. However, the interpretation is here rendered more probable, for it 

 has been shown that both types are producible within a single clone, 

 different cultures of the same clone yielding left overs of different type. 



The question at issue here is of theoretical importance. Does copula- 

 tion ever take place between cells that are physiologically as well as 

 morphologically and functionally identical? The preceding survey of the 

 conditions in various species and races of Chlamydomonas shows that 

 morphological and functional differences are frequently lacking, but that 

 at least in some of these cases physiological differences do exist when no 



