GLOSSARY 277 



Iris, the coloured part of the human eye surrounding the 

 pupil. 



Mutation, the origin of species by discontinuous variation (See 

 Variation, discontinuous). 



Prepotency, the property said to be possessed by certain in- 

 dividuals, especially amongst stalHons, of transmitting 

 their qualities to their offspring, whatever female they are 

 mated with. 



Pure, a term applied to those individuals which when mated 

 together produce, exclusively, individuals indistinguishable 

 from themselves. 



Recessive characters are those which, in a cross between in- 

 dividuals the two characters of each of which bear one of 

 the same Mendelian pair, entirely disappear in the first 

 hybrid generation. 



Reversion, the production, on crossing, 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). 



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



Somatic, of, or pertaining to, the body as opposed to the germ 



cells. 



Unisexual crosses, according to Prof, de Vries, are those between 

 two individuals, one of which bears a particular character 

 entirely lacking in the other {See Bisexual). 



Variation, the production by animals and plants of those differ- 

 ences the accumulation of which is supposed to have resulted 

 in the various forms of Hving things. Continuous variation 

 is the name given to the occurrence of such differences as 

 always exist in any sample of a given species. These varia- 

 tions are not supposed to be transmitted to the next genera- 

 tion. Discontinuous variation is the term applied to the 



