6o2 EVOLUTION, GENETICS, AND EUGENICS 



transmission devised by Charles Darwin. It implies the idea that the germ 

 cells are made up through the process of collecting from the blood stream 

 "gemmuJes" or representatives of all parts of the body. In this way each 

 structure of the adult parent would be present in the germ cell and would be 

 transmitted to the ofTspring. 



Panmixia. — An early theory of Weismann designed to account for the ru- 

 dimentation of structures; almost equivalent to cessation of natural selection. 



Parthenogenesis. — The development of an egg without fertilization. 

 A process in animals equivalent to Apogamy in plants. 



Peculiar. — A term used technically to describe a species or higher group 

 of organisms occurring in one region and nowhere else. 



Pedigree. — An ancestral history; a genealogical tree. 



Phenotype. — A group of individuals which are alike somatically and 

 look alike, but which may differ germinaily; the sum of the visible features 

 of an individual or a race. Contrast with Genotype. 



Phenotypic. — Pertaining to the somatic appearance of the individual 

 or group of individuals. Contrast with Genotypic. 



Phylogenetic. — Pertaining to the ancestral history of a group. Con- 

 trast with Ontogenetic. 



Phylogeny. — ^The history of the evolution of a species or a group, as 

 distinguished from Ontogeny. 



Preformation. — A theory that the individual is preformed in the egg 

 and needs only to grow or to unfold in order to reach its definitive state. 

 Contrast with Epigenesis. 



Protoplasm. — The living substance of cells. 



Pure line. — The descendants of a single individual that have not under- 

 gone any germinal change. 



Quadrumana. — An old name for apes and monkeys implying that their 

 hands and feet are both grasping appendages like hands. 



Recessive. — The opposite of dominant. 



Reduction division. — That division in germ cells when the chromosome 

 number is reduced from the diploid to the haploid condition; usually one 

 of the two maturation divisions of a germ cell. 



Segregation. — -The separation into separate gametes of the two members 

 of a pair of allelomorphs, resulting in gametes pure for one or the other of a 

 pair of allelomorphic genes. 



Serology. — That branch of experimental biology or medicine that deals 

 with the reactions of the blood to foreign materials and the production of 

 antibodies; the science of serums. 



Sex chromosome. — The particular chromosome (the X-chromosome, for 

 example) that seems to carry the factors for sex and through which sex is 

 inherited. 



Sex linked.— A term applied to characters located in the sex chromo- 

 somes. 



Sex ratio. — The relative proportion of the two sexes in a population 



