136 GLOSSARY 



Deviation. The amount by which an individual differs from the 

 mode in continuous variation. 



Dimorphism. The condition in which a species exists in two 

 distinct types or sharply separable varieties. "When the two 

 sexes differ thus, the condition is called Sexual Dimorphism. 



Dominant. "When two varieties, differing in one character, are 

 crossed together, and all the offspring have the character 

 borne by one parent, that character is dominant. Applied 

 to one of a pair of Mendelian allelomorphs. 



Egg -cell. The germ-cell produced by the female. 



Epistatic. "When one character A is superposed upon another B, 

 so that A prevents or obscures the appearance of B, al- 

 though they are not allelomorphic with each other, A is said 

 to be epistatic to B. 



c Extracted'' Homo zygote. "When two heterozygous individuals 

 are mated together, their homozygous offspring are spoken of 

 as ' extracted ' homozygotes. 



JF lt F 2 . The Symbol F 1 is used to indicate the offspring (first 

 filial generation) of a mating between two differing individuals. 

 The later generations (second, third filial, etc.) are repre- 

 sented by F 2 , Fo, etc. 



Factor. In Mendelian inheritance, the hereditary determinant 

 (q.v.) of a particular character is spoken of as the factor for 

 that character. 



Ferment. A body which has the power of causing chemical 

 action between substances which in its absence are inactive 

 towards one another. 



Fertilisation. The union of male and female germ-cells which 

 precedes the development of a new individual. It consists 

 essentially in the fusion of the nuclei of the germ-cells. 



Gamete. A germ-cell, q.v. 



Gemmules. Hypothetical bodies supposed to be given off by the 

 cells of the body, and entering the germ-cells, to transmit 

 heritable characters to the next generation. 



