GLOSSARY 



ACQUIRED, acquirement ; terms intended by biologists to indicate alterations in the 

 individual caused by the action of environment on his mind and body. Since, however, 

 all characters arise as a reaction to the environment the terms are misleading. They 

 really designate traits that arise under the stimulus of use and injury. 



ALLELOMORPH ; an ' alternative ' unit, believed by the followers of the Mendelian 

 hypothesis to exist in the germ-plasm, which is supposed to be compounded of such 

 units. 



BIOMETRY ; the measurement and statistical treatment of biological phenomena. 

 BI-PARENTAL ; see cell. 



CELL ; a living entity, usually microscopical, typically possessing a cell-wall, with living 

 protoplasmic contents (the cytoplasm} in which is embedded a nucleus. Within the nucleus 

 is a substance termed chromatin, which is differentiated from the rest of the nucleo-plasm. 

 Cells multiply by self-division, the mother-cell constricting itself and dividing into two 

 daughter-cells. Before division occurs the chromatin of the nucleus usually gathers itself 

 into masses termed chromosomes, the number of which is definite for each species. On the 

 nucleus depends, apparently, the nature of the cell, and therefore the nature of the in- 

 dividual that develops from the germ-cell. Consequently, it is probable that the nucleus 

 contains all or most of the germ-plasm, the substance which is the ' bearer of heredity,' 

 which carries the hereditary tendencies or developmental potentialities. The germ-plasm 

 has been identified with some show of reason with the chromatin. Unicellular animals 

 and plants consist each of a single cell, the daughter-cells of which separate and become 

 distinct individuals. Each cell therefore performs all the functions of life. On the other 

 hand, a multicellular organism is compounded of two or more cells. It takes origin in 

 a single cell (which is usually a fertilized ovum). The daughter-cells in the successive 

 generations do not separate. Consequently the individual may consist of billions of cells, 

 all of which are differentiated to perform special functions e.g. locomotion, secretion, 

 reproduction of new individuals (cell-communities). The cells of the multicellular organ- 

 ism which are immediately concerned with the reproduction of new individuals are 

 termed germ-cells. All the others (e.g. muscle, skin, and nerve cells) are termed somatic 

 cells, and together constitute the soma, the main mass of the body of the individual. 

 Since unicellular organisms are, in effect, germ-cells, they have, of course, no soma. The 

 germ-cells of multicellular organisms are termed sperms (spermatozoa) and ova. In the 

 case of plants they are termed pollen-grains and ovules respectively. Sperms are derived 

 from the male, ova from the female reproductive organs. A. fertilized ovum is formed 

 by the union of a sperm with an ovum. Apparently this act of conjugation consists 

 essentially in a union of nuclei which involves a more or less intimate union of the contained 

 chromatin. In some species each individual is an hermaphrodite ; that is, it possesses 

 both male and female organs and produces both sperms and ova. In the great majority 

 of species, including of course all those types the individuals of which are male or female 

 and produce only sperms or only ova, the germ-cells of the individual conjugate only 

 with germ-cells from another individual. The reproduction is then bi-parental. In some 

 species, however, there is self-fertilization ; that is the sperms and ova of the same 

 hermaphrodite conjugate. Some species produce only ova, which, without being fertilized, 

 develop into individuals. This mode of reproduction is termed parthenogenesis. Between 

 the germ-cell, fertilized or not, whence a multicellular individual is derived and the germ- 

 cells contained in his (or her) own body, lie generations of cells, the ancestors of the germ- 

 cells, which, like the cells of the soma, do not conjugate with other cells. These are the 

 generations of the germ-tract. When reproduction is by means of germ-cells it is 

 termed sexual; when it is by means of slips, buds, suckers, and the like, it is a-sexual. 



CELL-COMMUNITY ; see cell. 



CHARACTER ; any trait of an individual e.g. his head, a hair, the colour of a hair. 



CHROMATIN ; see cell. 



CHROMOSOME; see cell. 



CONJUGATION ; see cell. 



CYTOPLASM ; see cell. 



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