CHROMOSOME. So called on account of their affinity for certain dyes, the chromosomes are minute bodies seen in the divid ing cells of which the bodies of animals and plants are composed. Their characteristic configurations and remarkable behaviour in cell division, in the process of development, and in the union and formation of the reproductive elements has been the subject of a large body of research, since their discovery in 1873 by Anton Schneider, Flemming, Butschli and others. The progress achieved during the three decades that followed their discovery made it possible, when Mendel's law of segregation was rediscovered in the opening years of the present century, to identify the structural mechanism predicted by him. From that time to the present day, intensive study of the behaviour of the chromosomes in relation to breeding experiments have resulted in the building up of one of the most spectacular generalizations of modern biology. An exposition of this chromosome hypothesis is given in the article CYTOLOGY. The word was first used by Waldeyer (i888). (See also HEREDITY.) (L. T. H.)