Rnight —142— Dictionary 



Structural Hybrid. — One whose parental gametes differed 

 in respect of the structure of their chromosomes. It is 

 Fucentric when its dislocated segments have the same linear 

 sequence with respect to the centromere, Dyscentric when 

 they are relatively inverted (Darlington). 



Style. — An elongated part of the carpel between the ovary and 

 stigma. 



Sub-gene. — See under Step Allelomorphism. 



Sub-lethal. — Semi-lethal. See Lethal Factors. 



Subsexual Reproduction. — Parthenogenesis following ameio- 

 sis with non-reduction, but with segregation owing to crossing- 

 over (Darlington). 



Subspecies. — "The subspecies, or geographic race (q.v.), is a 

 geographically localized subdivision of the species, which 

 differs genetically and taxonomically from other subdivisions 

 of the species" (Mayr, 1942), 



Succession. — The lagging of the sex chromosomes behind 

 the autosomes in passing to the poles after meiosis. 



Succession, Law of. — The hypothesis that every species has 

 come into existence coincident, both in time and space, with 

 a pre-existing and closely allied species. 



Successional Speciation. — The gradual evolution of new 

 species from old over a long period of time. The characteris- 

 tic of this form of speciation is that a given type gradually 

 changes so that forms meriting new specific names eventually 

 emerge, later, differences of sufficient magnitude may arise 

 to necessitate new generic names. 



Superfemale. — A Drosophila fly or other insect having three 

 X chromosomes per double set of autosomes. 



Superfetation. — Superfoetation, q.v. 



Superfoetaticn. — Fertilization of a second ovum in a pregnant 

 animal after a considerable interval from the original concep- 

 tion; hypercyesis. 



Supermale. — A Drosophila fly or other insect having a single 

 X-chromosome per double set of autosomes. See Supersexes. 



Supernumeraries. — Inert chromosomes present in some, but 

 not in all, the members of a species. 



Super-reduction. — The production of pollen grains or ovules 

 with half, or approximately half, the normal gametic number 

 of chromosomes as a result of irregularities in nuclear division. 



Supersexes. — Individuals in the Insecta with an abnormal ratio 

 of X-chromosomes to sets of autosomes. See Superfemale 

 and Supermale. 



