134 



CARNEGIE INSTITUTION OF WASHINGTON. 



The following tabular statement suggests something of a typical 

 series of sex conditions among the sex-intergrade stock. It is merely 

 a stereotyped outline, however, and it should be remembered that in 

 the vast majority of individuals no such regular and coincidental 

 gradation of secondary sex-characters occurs, i.e., in this tabular out- 

 line approximately the same intermediate condition of maleness and 

 femaleness is assumed for every character of each individual of the 

 series, while as a matter of fact the correlation in the degree of male- 

 ness and femaleness of the different secondary sex-characters of the 

 same individual is frequently very low or even negligible. 



Table 4. 



'Typical series of sex-inter grades. Characters of first leg of sex-intergrade s and 

 of normal individuals of Daphnia longispina. 



Selection in intergrade stock. — It was noticed that the sex intergrades 

 of Simocephalus vetulus and Daphnia longispina showed a certain 

 amount of relationship between the degree of maleness of a mother 

 and the degree of maleness among her young. This suggested the 

 possibility of obtaining an effect of selection by using as a basis for 

 selection the degree of intergradeness among sibs in the same strain. 

 Selection was begun with 6 strains of the same line of Daphnia lon- 

 gispina. These 6 strains had originated from 6 of the 8 young of a 

 single brood of one of the original sex-intergrade mothers of this spe- 

 cies. Three of these strains were selected toward normal femaleness 

 and three toward intergradeness, the purpose being to make these as 

 divergent as possible. 



Selection was begun early in December 1917, and has been continued 

 without interruption since, covering from 34 to 40 generations in the 

 different strains. The data for only the last 16 generations of this 



