678 SEXUALITY 



two sexes differing by 20 percent or more in the production of either 

 cis or trans dimethyl crocetin, but not if they differ less than this. Fur- 

 ther, the intensity of the sex reaction (Table 9), as measured by the size 

 of clusters, also depends upon the difference in proportions of cis and 

 trans dimethyl crocetin produced by the two sexes under examination : a 

 difference of 20 percent results in the formation of pairs only (grade 

 one reaction); a difference of 30 percent yields clusters of 10 to 20 

 cells (grade 2); a difference of 40 percent or more yields clusters of 

 100 or more cells (grade 3) . 



By introducing capillary tubes filled with known mixtures of cis and 

 trans dimethyl crocetin into one edge of a drop of culture fluid and 

 adding gametes of a known sex to the opposite edge of the drop, Moewus 

 (1939b, 1939c) observed that the gametes aggregated at the open end 

 of the capillary tube whenever it contained cis and trans dimethyl cro- 

 cetin in proportions differing from those produced by the gametes by 19 

 percent or more, but not when the difference was less than this. More- 

 over, the time required to obtain at the mouth of the tube an aggrega- 

 tion of from 18 to 22 cells was from 200 to 254 seconds when the dif- 

 ference in proportions was 20 percent, 140 to 180 seconds when the 

 difference was 30 percent, and 80 to 109 seconds when the difference 

 was 40 percent. The speed of aggregation increased with increasing 

 cis/trans difference to 22 to 37 seconds with a difference of 90 percent; 

 hence the sex stuffs are chemotactic substances, and the grades of sex 

 reaction are indices of the speed of chemotaxis. Moreover, in any com- 

 bination of gametes that will copulate, each sex secretes chemicals that 

 attract the other and each reacts to the chemicals secreted by the other: 

 both gametes thus attract and both respond. 



INTERPRETATION OF THE SEXUAL PHENOMENA IN Chlamjdomonas 



The sexual phenomena in Chlamjdomonas have been interpreted by 

 Moewus and by Hartmann in accordance with Hartmann's (1929) theory 

 of sexuality. This theory may be formulated in the following series of 

 propositions: 



1. Sex is a universal biological phenomenon. 



2. There are always two and only two sexes. 



3. These two sexes are always male and female. 



4. Male and female are qualitatively diverse. 



