O. — Used to denote the absence of a sex chromosome e.g. XX 

 and XO as compared with the XX and XY system of sex 

 inheritance. 



Octonary Hybrid. — A hybrid obtained by crossing two differ- 

 ent quaternary hybrids such that all eight of its great-grand- 

 parents are different. 



Octoploid. — Having eight haploid sets of chromosomes in the 

 somatic cells. 



Oestradiol. — An ovarian hormone which controls oestrus. 



Ooestradiol dipropionate, — benzoate, — ethinyl. — See 

 under Oestrogens. 



Oestrin. — Sometimes used in the sense of any oestrogen but 

 usually restricted to natural oestrogens belonging to the steroid 

 group {cj. Robson). 



Oestrin-withdrawal Theory of Menstruation. — The theory 

 that the fall in the oestrin level is the essential factor in the 

 genesis of all types of menstrual bleeding (Robson). 



Oestriol, — glucuronide. — See under Oestrogens. 



Oestrogenic Substances. — Oestrogens, q.v. 



Oestrogens. — A group of hormonic substances, some natural 

 and some synthetic, which are able to bring about oestrus. 

 The following are included in this group: Oestradiol, — ben- 

 zoate, — dipropionate, — ethinyl, Oestrone, Oestriol, — 

 glucuronide, Stilboestrol, — dipropionate, Hexoestrol, Tri- 

 phenyl-chloro-ethylene. 



Oestrone. — See under Oestrogens. 



Oestroscope. — An instrument for measuring the viscosity of 

 the cervical mucus which closes the os uteri. The oestroscope 

 detects the onset of oestrus since the viscosity of the cervical 

 mucus reaches its minimum at oestrus. 



Oestrus. — The period of sexual desire in animals; rut. 



Offset. — A side shoot used as a means of vegetative propaga- 

 tion. 



Oleosome. — Any fatty inclusion in the cytoplasm. 



Oligandrous. — With few stamens; oligostemonous. 



