riddle: control of sex ratio 341 



are white in color). (2) Females hatched from eggs laid earlier 

 in the season are more masculine in their sex behavior than are 

 their own full sisters hatched later in the season. And, several 

 grades of females can be thus seriated according to season of hatch- 

 ing. (3) The female hatched from the first egg of the clutch is 

 more masculine than her sister hatched from the second of the 

 clutch in a great majority of the cases. And in nearly all these 

 latter matmgs the more masculine bird is so predominantly 

 mascul ne that she takes the part of the male a full 100 per cent 

 of the time in copulating with her very feminine clutch-mate 

 sister. (See Riddle, '14a). 



I may remark in passing that the effect of testicular and ovar- 

 ian extracts (suspensions) have been studied in connection with 

 the work on sex-behavior. The results have clearly shown 

 that the sex behavior of a pair of females is modified by the 

 intra-peritoneal injection of testis (pigeon) extract into the one 

 and ovarian (pigeon) extract into the other. In one case, for 

 example, the more "feminine" female of a pair was given testis 

 extract and her more "masculine" mate received ovarian ex- 

 tract. After the injections the bird formerly more feminine, 

 16 copulations as a male to 23 by her consort, became very 

 much the more masculine, 27 copulations as a male to onlj' 2 

 by her consort. 



To one other kind of fact concern ng the effects of reproduc- 

 t've over-work n changing the developmental and sex phen- 

 omena of the germs of the later part of the season, we ask a 

 moment's consideration. 



It has been found that some females dead at relatively ad- 

 vanced ages show persistent right ovaries. The right ovary 

 in pigeons normally begins degeneration at or before hatching 

 and is usually wholly absent from the week-old squab. In 

 our study it soon became evident that the persistent right ovar- 

 ies were found almost exclusively in birds hatched from eggs 

 of overworked series. Further study has shown in addition 

 that they arise almost wholly from the eggs of autumn, and 

 predominantly then from the second eggs of the clutch — that 

 is from eggs otherwise known to have greatest or strongest 



