DEPARTMENT OF EXPERIMENTAL EVOLUTION. 133 



and related genera. During the year in review, the work with those 

 individuals which show an intergrading or intermediate sex has been 

 developed in two directions: (1) a detailed analysis of various degrees 

 of intergrading as affecting a secondary sex character of Daphnia 

 longispina; (2) the continuation of the selection experiment of the 

 sex-intergrade strains of Daphnia longispina. 



Analysis of degrees of sex inter gradedness. — As has been said in 

 previous reports, Dr. Banta finds that the sex-intergrades are not 

 gynandromorphs in that they are not sexual mosaics, but that in the 

 intergrades the male and female influences are blended to various de- 

 grees in the different parts of the body, as revealed by the several 

 secondary sex-characters. A careful study of a secondary sex-char- 

 acter, the first leg, has shown clearly that this interpretation is correct 

 and that there is an almost endless variety of conditions of sexual 

 significance in this complicated appendage, which may exist in any 

 condition between that of the fully developed male and that of the 

 fully developed female. This first leg in the normal female has the 

 following simpler salient features: (1) only a single flagellum-like 

 terminal filament to the No. 2 element, which element does not possess 

 a hook nor have a swollen hairy base; (2) further, this appendage in 

 the normal female has its third element terminated by three filaments. 

 In the male, on the other hand, (1) the second element has two terminal 

 filaments and has a large, swollen base coarsely hairy on one side, from 

 which is developed a relatively large stout hook almost as long as the 

 remainder of the element, and moreover (2) the third element is termi- 

 nated by four filaments. Between these two conditions, that typical 

 for the normal female and that typical for the normal male, there is 

 every conceivable intermediate condition of development. These 

 intermediate conditions of development may be thought of as the 

 results of the various degrees of female and male influences operative in 

 different individual cases and in different parts of the same intergrade 

 individual; e.g., it is of interest to note that the two legs of the same 

 pair in the same individual daphnid may differ slightly or largely in 

 the degree of femaleness and maleness revealed in their morphological 

 structure. One appendage may be normally female, while its mate is 

 slightly or largely male in character. 



Further, the degree of femaleness and maleness of one or both of the 

 first legs may be quite unhke the degree of maleness and femaleness 

 of the other secondary sex-characters of the same individual. How- 

 ever, it is true that if a certain secondary character is highly male 

 (or female), the other secondary sex-characters are likely to be male 

 (or female) to a somewhat similar degree. But, on the whole, the 

 correlation in degree of maleness (or femaleness) between the different 

 secondary sex-characters in an individual is not very large and in 

 many cases not even apparent. 



