GLOSSARY OF TECHNICAL TERMS xxxi 



ORGAN (Lat. organum, implement), a specialised part of a living 



body concerned in some particular function. 

 ORGANELL^E (Lat. dim. organum, implement), a term sometimes 



applied to the organs of unicellular organisms. 

 ORGANISM (Lat. organum, implement), that which has organs, viz., 



a living body. 

 OSMOSIS (Gr. wo-juo?, pressure), the diffusion of dissolved substances 



through semi-permeable membranes (upon which they exert 



a pressure). 

 OVARY (Lat. ovum, egg), in animals the female gonad, the organ in 



which eggs are produced ; in higher plants the part of the 



flower in which the immature seeds (ovules) are produced. 

 OVIDUCT (Lat. ovum, egg ; ductus, conduit), the tube or duct 



through which the eggs pass to the exterior of the body. 

 OVOTESTIS (Lat. ovum, egg ; testis, testicle), a gonad which 



produces both male and female gametes. 



OVULE (Lat. dim.o#Mw,egg),the immature seed of a flowering plant. 

 OVUM (Lat., egg), a female germ cell or gamete. 

 P^DOGENESIS (Gr. irais, child ; yeWo-i?, birth), the partheno- 



genetic production of offspring by immature females. 

 PALAEONTOLOGY (Gr. TtaXaios, ancient; ov, OVTOS, being; Xoyos, 



discourse), the science of fossil organisms. 

 PALAEOZOIC (Gr. ira\ai6s, ancient; for/, life), the name given to 



one of the principal periods of the earth's history, in which 



ancient forms of life existed. 

 PALINGENETIC (Gr. -na\iv, backwards [should be TraAeuos, ancient] ; 



yev(ris, origin), of ancient origin. 

 PANGENESIS (Gr. -nav, all, every; ytvea-is, origin), the name given 



by Charles Darwin to hL theory of heredity, in accordance 



with which every cell of the body contributes something 



towards the formation of the germ cells. 



PARAPHYSES (Gr. iiapafyvvis, that which grows alongside), hair- 

 like structures which grow amongst the reproductive organs 



(in Fucus, &c.). 

 PARASITE (Gr. Trapcuriros, one who lives at another's table), an 



organism which nourishes -itself at the expense of another 



living organism without making any return. 

 PARENCHYMA (Gr. Ttap<yyvv< a i filling material), a kind of ground 



tissue in which various organs are imbedded. 

 PARIETAL (Lat. paries, wall), one of the bones of the skull, hence a 



region of the head. 



