O — 107 — Orientation 



Oligocarpous. — With few carpels. 



Oligogenes. — Major genes controlling qualitative characters 

 which show normal mendelian inheritance. 



Oligopyrene. — Of spermatozoa: having less than the normal 

 complement of chromosomes. 



Oligospermous. — Producing few seeds. 



Oligostemonous. — With few stamens; oligandrous. 



Oligotokous. — Producing few young. 



Ontogeny, Ontogenesis. — The developmental history of an 

 individual from fertilized egg to adult organism. Adj. Onto- 

 genetic. 



Ooblastema. — A fertilized ovum, 



Oocentre. — The division centre of an ovum. 



Oocyte. — The egg mother-cell from which are produced, by 

 the first meiotic division, the secondary oocyte and the polar 

 body. The secondary oocyte is functional, the polar body 

 generally divides once and the daughter polar bodies dis- 

 integrate. 



Oogamy. — The fusion, in fertilization, of gametes of unequal 

 size, typically a large female gamete and a small active male 

 gamete. Adj. Oogamous. 



Oogenesis. — The origin and development of female gametes 

 by maturation divisions from an ovary. 



Oogonium. — (i) The female sexual apparatus of the algae 

 and fungi, (ii) A cell from which primary oocytes are pro- 

 duced by mitosis. 



Ookinesis. — The mitotic phenomena in the egg-cell during 

 maturation and fertilization (Whitman; Wilson). 



Ooplasm. — The cytoplasm of the oocyte or ovum. 



Oosperm. — A fertilized egg; ooblastema. 



Oosphere. — A female gamete prior to fertilization. 



Oospore. — A fertilized ovum; oosperm; ooblastema. 



Ootid. — The haploid egg cell after meiosis. cf. Spermatid. 



Organic Selection, Theory of. — The hypothesis that an 

 organism may become genetically adapted to particular condi- 

 tions by first undergoing non-heritable modification so that 

 any subsequent mutations which are favourable to the new 

 conditions of life tend to be selected and fixed. 



Organogenesis, Organogeny. — The differentiation and de- 

 velopment of organs. 



Organophyly. — The developmental origin of organs. 



Orientation. — The movement of chromosomes so that their 

 centromeres lie axially with respect to the spindle, either as 

 to their potential halves at mitosis (auto-orientation) or as 



