608 EVOLUTION, GENETICS, AND EUGENICS 



Sexual reproduction. — That mode of reproduction that involves the 

 union of gametes to form a zygote. Same as Gametic reproduction. 



Simian. — Pertaining to apes. 



Soma. — The body of an organism as contrasted with the germ cells. 



Somatic. — Pertaining to the body. Contrast with Germinal. 



Somatoplasm. — Same as Soma. Contrast with Germ plasm. 



Special creation. — A popular doctrine holding that all species existing 

 today were created by divine fiat within a few days and that they have not 

 materially changed. 



Species.— A group of varieties or a single variety which, in botanical or 

 zoological characters and genetic relationship, can be differentiated from all 

 other groups or varieties. 



Sperm. — A short term for the male gamete. 



Spermatozoon. — The longer technical term for the functional male 

 gamete. 



Sporadic. — Occurring singly, scatteringly, or apart from others of the 

 same kind. 



Symbiosis. — See Commensalism. 



Systematist. — A taxonomist or specialist in the science of classification. 



Synapsis. — The pairing off and lying together of homologous chromo- 

 somes, prior to the maturation division. 



Taxonomy. — The science of classification. 



Teleology. — 'The doctrine that the processes of nature were originally 

 purposed or planned; the doctrine of design. 



Tetraploidy. — That chromosomal condition where the germ cells in some 

 way acquire four times the haploid number of chromosomes; thus some so- 

 called plant mutants are tetraploid. 



Trihybrid cross. — A hybridization experiment in which the parents differ 

 with regard to three pairs of allelomorphs. 



Triploidy. — That chromosomal condition where the germ cells in some 

 way acquire three times the haploid number of chromosomes; some so-called 

 plant mutants are triploid. 



Uniformitarianism. — The theory that the changes of the past may be 

 interpreted in terms of the changes of the present, a.nd that most changes 

 are of a slow, gradual kind. Contrast with Catastrophism. 



Variety.- — -A group of individuals within a species which resemble one 

 another but differ in some respects from other members of the species. 



X-chromosome. — The so-called sex-chromosome. 



Y-chromosome. — The chromosome that usually pairs off with the X- 

 chromosome in synapsis. It does not seem to carry any genetic factors 

 except possibly that of fertility. 



Zygote. — A combination germ cell formed by the fusion of two gametes; 

 the individual, with the diploid number of chromosomes, that result from 

 the development of a fertilized egg. 



Zygotically. — Pertaining to the zygote or fertilized egg. 



