SEXUALITY 669 



capable of copulating by subjecting them to filtrates from gamete cul- 

 tures of the Coimbra race of the same species. (See 675 et seq. 

 for a further account of these filtrates. ) However, filtrates from any one 

 Coimbra clone would activate some of the Giessen clones, but not all. 

 The remaining Giessen clones required for activation treatment with a 

 filtrate from a different Coimbra clone, one which would copulate with 

 the first Coimbra clone. The Giessen gametes would now copulate only 

 if a clone activated by the one filtrate was mixed with a clone activated 

 by the other filtrate. Thus the Giessen clones are of two diverse physio- 

 logical types, and copulation occurs only between the two types, not 

 between gametes of the same clone. 



In all the races thus far considered, there are regularly physiological 

 differences between copulating gametes, which are invariably members 

 of different clones. In the remaining three races investigated by Moewus 

 (1934, 1938a), C. eugameios f. subheteroica and f. synoica and C. 

 dresdenis, copulation occurred regularly among gametes of any one 

 clone. Among these three races, the situation in C. eugametos f. sub- 

 heteroica is unique. In any culture relatively few cells copulate. If the 

 cells left over after copulation has ceased in a culture are mixed with 

 the left overs from cultures of other clones, some of the mixtures will 

 exhibit typical copulation. Exhaustive analysis of many clones shows 

 that the same results hold here for the left overs as for entire clones of 

 the species previously discussed. The left overs of any one clone are 

 always of the same physiological type, but other clones yield left overs 

 of a different type. There are just two kinds of clones, differing in the 

 type of left overs they produce. Left overs of one type copulate only 

 with left overs of the other type. 



From these observations, Moewus (1934) concludes that each clone 

 produces both types of gametes, but always one in much greater fre- 

 quency than the other. Some clones regularly produce mostly one kind 

 of gamete; other clones regularly produce mostly the other kind of 

 gamete. Copulation then takes place within a clone until all the rarer 

 type of gametes have found partners, so that all the left-over cells are 

 of the prevailing type. Moewus (1934) reports that the behavior of 

 this race can be made to simulate that of those previously discussed by 

 subjecting the cultures to very dilute formalin or acetaldehyde. With 

 this treatment, the cultures no longer yield copulation within a clone, 



