Knight — 110 — Dictionary 



Palingeny. — Repetition of ancestral forms during embryony. 



p-amino benzoic acid. — A component of the vitamin Bg 

 complex. 



Pangamy. — Indiscriminate or random mating. Adj. Pan- 

 gam ic. 



Pangenesis, Theory o£. — Darwin's theory that gemmules, 

 collected from the organs into the germ cells, are dispersed 

 again to corresponding organs for whose nature they are 

 responsible (Shull). 



Pangens. — Darwin's hypothetical particles controlling in- 

 heritance. See Pangenesis, Theory of. 



Panmictic Unit. — A local population in which there is com- 

 pletely random mating. 



Panmixia. — (i) Random inbreeding with no selectivity and 

 unaffected by natural selection, (ii) The cessation of the 

 effect of natural selection. 



Panmixie. — Panmixia, q.v. 



Pantothenic Acid. — A component of the vitamin Bg complex. 



Parabiotic Twins. — Animals (typically Amphibia) which 

 have been grafted together, in the embryonic stage, so that 

 the subsequent development of each is potentially able to be 

 affected by the hormones developed by the other. 



Paracentric Inversion. — An inversion which, being located 

 entirely within one chromosome limb, does not involve the 

 centromere. 



Paracme. — The phase in the developmental history of a race 

 or of an individual when vigour is waning. 



Paradesm, Paradesmose, Paradesmus. — An extra-nuclear 

 filament connecting the division centres in the mitosis of 

 flagellates (Kafoid & Swezy; Wilson). 



Parageneon. — A species with relatively little morphological 

 or genetical variation throughout its range but which con- 

 tains some aberrant genotypes; all its individuals are inter- 

 fertile (Camp & Gilly). 



Paragenesis. — Fertility as between a hybrid and one or both 

 of its parents the hybrid being otherwise sterile. 



Paralinin. — The ground-substance of a nucleus. 



Parallel Mutations. — Closely similar mutations occurring in 

 two or more species of the same genus, and affecting homolo- 

 gous genes and homologous processes. Sometimes mutations 

 involving homologous processes but non-homologous genes are 

 included under parallel mutations. 



Paranuclein. — The substance of which nucleoli are composed. 



