Phytogeny. — The history of the evolution of a species 

 or group, distinguished from ontogeny. 



Pure Line. — A group of individuals derived solely by 

 one or more self-fertilizations from a common homozygous 

 ancestor. 



Prepotency. — The property said to be possessed by cer- 

 tain individuals, especially amongst stallions and bulls, of 

 transmitting their qualities to their offspring whatever 

 female they are mated with. 



Reduction Division. — One of the last two divisions in 

 gametogenesis, when homologous chromosomes are dis- 

 sociated and pass into different gametes. 



Recessive Characters. — Those which, in a cross between 

 individuals the two characters of each of which bear one of 

 the same Mendelian pair, entirely disappear in the first hy- 

 brid generation. 



Reversion. — The production, on crossing, of one or 

 more characters of a supposed remote ancestor of the two 

 forms crossed. 



Segregation. — The reappearance in definite ratios, in 

 the second hybrid generation, of the characters of two forms 

 crossed; and of the first hybrid generation (where this 

 differs from the dominant character). 



Sex-chromosome. — The accessory chromosome which 

 has come to be associated with one or the other sex, or one 

 member of a pair of morphologically or physiologically dis- 

 tinct chromosomes which carry a factor or factors for sex. 



Sex-linked. — Applied to factors located in the sex-chro- 

 mosomes or to the characters conditioned by them. 



Sex-ratio. — The proportion of males and females in a 

 population. 



Soma. — The body, as opposed to the germ cells. 



Synapsis. — The conjugation of maternal and paternal 

 chromosomes preceding the reduction of division. 



Unit Characters. — Characters which behave as units in 

 heredity. 



Zygote. — The result of the union of two gametes (See 

 Gamete). 



HO 



