440 SUMMARY OF CURRENT RESEARCHES RELATING TO 



present higher and higher storage, i.e. the earlier dutches store less — are 

 more male-like ; the later ones all store more — are more female-like ; 

 and the eggs of the low-storage period give rise (in the generic cross) 

 to males, and those of the high-storage period produce females. 



" The progressive increase in storage capacity of the eggs during the 

 season — under overwork — is to be interpreted as a decrease in the oxidiz- 

 ing capacity of these same eggs. Living cells in general dispose of 

 ingested food material by storing it or by burning it. If oxidized, the 

 products of the oxidation are removable, and do not serve to increase the 

 bulk of the cell. The low-storage capacity of the male-producing eggs as 

 compared with the high-storage capacity of female-producing eggs, is 

 therefore, an index of higher oxidizing capacity, or, as more usually stated, 

 a higher metaholism of the male-producing eggs as compared with the 

 female-producing eggs." There is also some evidence (with exceptions) 

 that the male-producing ovum has a higher percentage of water than 

 does the female-producing ovum, and it is plain that the more hydrated 

 state of the colloids favours a higher rate of oxidizing metabolism, while 

 the less hydrated state favours increased storage. 



An estimate of energy- values of the yolks, determined by the calori- 

 meter, confirms the conclusions otherwise reached. Curious corrobora- 

 tions are also afforded by studies in sex-behaviour. Thus, females 

 hatched from eggs laid earlier in the season are more masculine in their 

 sex-behaviour than are their own full sisters hatched later in the season. 

 Several grades of females can be thus seriated according to the season 

 of hatching. The female hatched from the first Qgg of the clutch is 

 more masculine than her sister hatched from the second of the clutch in 

 a great majority of cases. Another curious point is the frequency in the 

 persistence of the right ovary in birds hatched from eggs otherwise known 

 to be most feminine. 



There is clear evidence that sex and such characteristics as fertility 

 and developmental energy not only bear initial relations to the order of 

 the egg in the clutch, but that sex and these other characteristics are 

 progressively modified under stress of reproductive overwork, until at the 

 extreme end of the season certain feminine features are abnormally 

 or unusually accentuated. Thus sex reveals itself as a quantita- 

 tive modifiable character, associated with modifiable metabolic levels. 

 Femaleness in the egg is associated with low metabolism, lower per- 

 centage of water, and higher total of fat and phosphorus, or of phos- 

 phatides ; and conversely for maleness. Analyses of the blood of adult 

 birds go to show that the metabolic differences of male and female germs 

 persist in the male and female adults. 



The agreement between Riddle's experimental results and the inter- 

 pretations offered by Geddes and Thomson in " The Evolution of Sex " 

 (1889) is remarkable. The author writes : " A general classification of 

 male and female adult animals on the basis of a higher metabolism for 

 the one and a lower for the other, was indeed made by Geddes and 

 Thomson many years ago. It now seems beyond question that this 

 conclusion of these authors is a correct and important one." 



The author refers to the fact that the extent of the modifiability of 

 an animal by internal secretions, which modify the metabolism, is, in 



