6oo EVOLUTION, GENETICS, AND EUGENICS 



Heterozygous. — Having the allelomorphic pairs composed of dissimilar 

 elements, resulting in the production of more than one kind of gametes. 



Heterozygous sex. — The sex in which the members of the chromosome 

 pair that determines sex are unlike. 



Homologous structures. — Any two structures either in the same or in 

 different individuals or species that arise from equivalent embryonic rudi- 

 ments and have the same structural relations to other parts, irrespective of 

 the function subserved. Contrast with Analogous structures. 



Homozygote. — An individual or a zygote resulting from the union of like 

 gametes. 



Homozygous. — Having the allelomorphic pairs composed of similar ele- 

 ments, resulting in the production of only one kind of gamete. 



Homozygous sex. — The sex in which the members of the chromosome 

 pair that determines sex are alike. 



Hormone. — A substance, secreted by one of the endocrine glands, that 

 affects the development of or the functioning of some other part or parts of 

 the body. 



Indigenous. — ^Living naturally in any country or climate. Contrast 

 with Introduced. 



Induction. — Any change in a germ cell or an embryo that persists for 

 only a few generations and then disappears. Contrast with Mutation. 



Introduced. — Brought in from another coimtry and living more or less 

 successfully under foreign conditions. Contrast with Indigenous. 



Isolation. — The process of separating one section or strain of a species 

 from another section or from the main body of the species; believed to 

 facilitate the establishment of new species. 



Lamarckian. — Pertaining to Lamarck's doctrine of the inheritance of 

 acquired characters. 



Lamarckism. — The theory of the inheritance of acquired characters. 



Larva. — A self-supporting embryo; a developmental stage of an animal 

 in which various adaptive structures for self-support appear that may or 

 may not be significant for the development of adult structures. 



Lethal. — Producing death; destructive of life. 



Linin. — ^An achromatic or non-chromatin substance that forms a net- 

 work of threads in the nucleus. 



Linkage. — The type of inheritance in which genes (factors) tend to 

 remain together in transmission from generation to generation, owing to 

 their location in the same chromosome. 



Locus {pi. loci). — A definite point or region in a given chromosome at 

 which is located a genetic factor or gene. 



Maturated germ cell. — See Gamete. 



Maturation. — The process through which germ cells pass in preparation 

 for fertilization, usually resulting in the formation of gametes. 



Mitosis. — The normal process of cell division, involving the formation 



