COURTSHIP AND SEX 237 



intensity of their chemical processes, and are respectively 

 male-producing and female-producing. 



Riddle's Experiments. — Professor Oscar Riddle has found 

 that the ova of the pigeon are dimorphic. That is to 

 say, there are male-producing ova and female-producing 

 ova, distinguishable from one another. 



The male-producing egg of the spring is an eg^ that 

 stores less material than does the female-producing egg of the 

 autumn. The male-producing egg of a clutch stores less 

 material than does its female-producing neighbour. The 

 eggs of old females store more material than do those of birds 

 not so old, and they yield a higher percentage of female 

 offspring. 



Thus it is evident that the egg of female-producing 

 tendency is one whose storage metabolism is high as compared 

 with the eggs of male-producing tendency. Moreover, the 

 chemical analyses show that during the season successive 

 clutches present eggs with higher and higher storage. The 

 earlier clutches store less and some experiments showed that 

 they tend preponderantly to develop into males. The later 

 clutches all store more, and the same line of experiments 

 showed that they tend preponderantly to develop into 

 females. 



The contrast between the two kinds of eggs must be 

 stated more precisely. " The progressive increase in storage 

 capacity of the eggs during the season — under overwork — 

 is to be interpreted as a decrease in the oxidising capacity 

 of these same eggs. Living cells in general dispose of 

 ingested food by storing it or by burning it. If oxidised, 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 oxidising capacity, or, as more usually stated, a higher 

 metabolism 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 the female-producing ovum, and 



