242 THE BIOLOGY OF BIRDS 



Professor M. F. Guyer has been led (191 6) to regard the 

 males as homozygous and the females as heterozygous for 

 sex and sex-linked characters. 



Physiological View. — We adhere to the view of sex 

 expounded in " The Evolution of Sex," in 1889, that the 

 deep constitutional difference between the male and female 

 organism, which makes of the one a sperm-producer and 

 of the other an egg-producer, is due to an initial difference 

 in the balance of chemical change. The female seems to be 

 relatively more anabolic or constructive, the male relatively 

 more katabolic or disruptive. 



A young germ-cell has, metaphorically, an alternative 

 between two different, but equally viable, lines of life — the 

 male and the female. It may have in its chromosome 

 equipment an original bias in the one direction or in the other ; 

 or it may be shunted on to one line or the other by the sui"- 

 rounding conditions — nutritive especially. Influences which 

 favour a preponderance of anaboHc processes, which affect 

 the nucleo-cytoplasmic relation in a manner favouring 

 cytoplasmic assimilation, will tend to the increase of female- 

 producing eggs. Influences that operate in the opposite 

 direction will favour the increase of male-producing eggs. 



