668 SEXUALITY 



one. This same functional difference occurs also in those pairs that differ 

 markedly in size in C. eugametos; but not in the usual pairs, in which 

 the gametes are alike in size (Moewus, 1933). Nor does it appear in 

 other species in which the gametes are morphologically isogamous. Func- 

 tional differentiation thus appears to be strictly correlated with morpho- 

 logical differentiation, occurring only when one gamete is flagellated and 

 the other not, or when one is much larger than the other. Further, both 

 morphological and functional differentiation may exist between gametes 

 in some copulating couples and not in others of the same species (C. 

 eugametos, Moewus, 1933). 



Physiological differences between gametes. — In this section will be 

 given only the general evidence of physiological differentiation between 

 gametes, reserving for later consideration the question of the nature of 

 such differentiation. If copulating gametes are not diverse physiologically, 

 then any two gametes can copulate with each other; but if they are regu- 

 larly diverse, there must be at least two kinds of gametes, with copula- 

 tion taking place between gametes of different types. The basic question, 

 therefore, is simply whether or not any two gametes of a species can 

 copulate with each other. 



In some species and varieties (C. cocci f era, C. braunii, C. paupera, 

 C. eugametos f. typica and simplex, C. paradoxa, and C. pseudopara- 

 doxa from Coimbra, Portugal; Moewus, 1933; Hartmann, 1934; 

 Moewus, 1936, 1937b, 1938a), the answer to this question is simple 

 and definite. Gametes produced within a clone do not copulate with 

 each other, but they do copulate with gametes produced by certain other 

 clones. In these races, therefore, the copulating gametes must always 

 be physiologically diverse. Moreover, this diversity is not invariably 

 associated with morphological or functional diversity, for five of the 

 seven races showing this phenomenon have morphologically and func- 

 tionally isogamous gametes. 



To the same category belongs a race of C. pseudoparadoxa, from 

 Giessen; but the physiological difference is less apparent, requiring 

 special methods to bring it to light. In this race, copulation does not 

 normally occur either between gametes of the same clone or between 

 gametes of different clones. Gametes of C. pseudoparadoxa are recog- 

 nizable by their small size. Moewus (in Hartmann's article, 1934) found 

 that the noncopulating gametes of the Giessen race could be rendered 



