Homology — 75 — Hyperchimaera 



Homozygous Sex. — The homogametic sex; that sex which 

 produces gametes of only one kind with regard to their proper- 

 ties of sex determination. See X- and Y-chromosomes. 



Hormone. — A hormone is a product of animal metaboHsm, 

 effective in very small amounts, produced by special endocrine 

 glands and active on the organism itself in a very specific 

 manner (Schopfer). 



Horotelic. — Evolving at a certain modal rate, as opposed to 

 Bradytelic (evolving considerably slower than the modal rate) 

 and Tachytelic (evolving much faster than the modal rate). 



Hyaloplasm. — The clear, non-granular protoplasm of a cell 

 in which the cytomicrosomes are suspended. 



Hybrid. — The product of a cross between individuals of un- 

 like genetic constitution. See, also, Numerical — and Struc- 

 tural — . 



Hybrid Cline. — Northocline; an extension of the term cline 

 {q.v.) to cover the gradation of forms which occurs in nature 

 following inter-specific hybridization. 



Hybrid Swarm. — A hybrid population typically occurring in 

 the overlapping area between inter-fertile species or sub- 

 species. 



Hybrid Vigour. — The increased vigour often exhibited by 

 hybrid individuals; heterosis. 



Hybridism. — The state of being hybrid. 



Hybridization. — The crossing of individuals of unlike genetic 

 constitution. See Allopatric — and Sympatric — . 



Hybridization, Introgressive. — Hybridization in which in- 

 filtration of the germplasm of one species into another occurs; 

 typically such infiltration is brought about by chance back- 

 crossing. 



Hybridogenous Pseudo-parthenogenesis. — Seed produc- 

 tion following stimulation by pollen the male nucleus of which 

 becomes eliminated before fertilization so that a maternal 

 embryo is formed which, as a result of doubling, is diploid. 

 (In some of these cases it has been shown that the endosperm 

 is of hybrid origin although the embryo is purely maternal). 



Hydrophilous. — Water-pollinated. 



Hydroxyprogesterone. — A hormone secreted by the corpus 

 luteum in the ovary and controlling events in pregnancy (Mot- 

 tram, 1944). 



Hygroplasm. — The more liquid portion of protoplasm. 



Hyperchimaera. — A chimaera whose components are not 

 arranged in sectors but are agglomerated to form a mosaic. 



