360 ABSTRACTS OF PAPERS. [VOL. II. 



was evident in the number, arrangement and correlation of 

 the otocysts, no attempt has been made to ascertain the exact 

 ratio, owing to the difficulty attending this determination in 

 preserved specimens. 



The following summary will express in a general way some 

 of the more evident conclusions reached : 



1. Variation among Hydromedusae is of wider extent than 

 had been suspected. 



2. It is much greater in some genera than in others. 



3. It seems to be much less symmetrical and correlated 

 than among Scyphomedusae. 



4. Many phases of variation appear to be wholly devoid 

 of correlative and adaptive aspects. 



XXIV. EXPERIMENTS ON MODIFYING THE 



NORMAL PROPORTION OF THE SEXES 



IN THE DOMESTIC FOWL. 



GEORGE WILTON FIELD. 



THIS is a brief report on a series of experimental attempts 

 to ascertain the factors which determine sex. 



The normal proportion given by Darwin from observation of 

 100 1 chicks during eight years was 94.7 males to every 100 

 females. From 2105 chicks during two years, we found the 

 proportion to be 80.6 males to every 100 females. 



These figures lead us to query whether the normal propor- 

 tion may not have changed during the past forty years as a 

 result of the breeders' desire to produce a larger proportion 

 of females. 



In the experiments attempts were made to isolate the factors 

 so that the effects of each could be observed: 



i . Absolute age of parents : 



9 young females mated to male of same age. 



2. Relative age of parents : 



9 old females mated to young male. 

 9 young " " " old " 



