One: Descriptive.- I. Meiosis in Male Chorthippus.- II. Patterns of Variation in Chiasma Formation.- 1. Localisation.- 2. Achiasmate Meiosis.- 3. Female Meiosis.- III. Structural Abnormalities at Meiosis.- 1. Chromosome Breakage.- 2. Side-arm Bridges.- a) Properties of the Side-arm Bridges.- b) Sub-chromatid Exchange.- 3. Univalence and Mis-division of the Centromere.- 4. Meiotic Mosaics.- IV. Structural Variants.- 1. Meiosis in Structural Hybrids.- a) The Inversion Heterozygote.- b) The Inverted Duplication.- c) The Interchange Heterozygote.- d) Centric Fusion and Fission.- 2. The Meiotic Behaviour of Abnormal Chromosomes.- a) Dicentric Chromosomes.- b) Ring-chromosomes.- V. Meiosis in Numerical Mutants.- 1. Haploids.- 2. Aneuploids.- 3. Polyploids.- a) Meiosis in Autopolyploids.- b) Meiosis in Allopolyploids.- c) Meiosis in Polyploid Interchange Heterozygotes.- d) Secondary Pairing in Allopolyploids.- VI. Meiosis in Organisms with Non-localised Centric Systems.- 1. The Polycentric Compound Chromosomes of Parascaris.- 2. The Holocentric Chromosome.- VII. Meiosis in Species Hybrids.- VIII. Meiotic Behaviour of Special Chromosomes.- 1. Sex-chromosome Systems.- 2. B-chromosomes.- Two: Analytical.- I. Chromosome Duplication and Pairing.- II. Chiasma Formation.- 1. General Features.- 2. The Mechanism of Crossing-over.- III. Coiling.- 1. Patterns of Coiling.- 2. The Basis and Mechanism of Chromosome Coiling.- 3. Allocycly.- 4. Chiasma Terminalisation.- IV. Chromosome Movement and Segregation.- 1. Random Distribution.- 2. Systems of Non-random Distribution.- V. The Control of Meiosis.- 1. The Analysis of Meiotic Variation.- a) Between Species.- b) Between Sexes within Species.- c) Between Individuals within "Sexes" and Species.- d) Between Cells within Individuals.- e) Between Nuclei within Cells.- f) Between Chromosomes within Nuclei.- g) Between Parts of Chromosomes.- 2. The Characterisation of Meiosis.- 3. Provision for Division.- a) DNA, RNA and Protein Synthesis in the Normal Meiotic Cycle.- b) Origin of the Deoxyribosidic Pool.- 4. Controlled Meiotic Anomalies.- 5. Additional Division Requirements.- 6. The Developmental Control of Meiosis.- a) The Suppression of Meiosis and the Failure of its Products in Normal Individuals.- b) The Synchronisation of Meiosis.- c) The Reversible Arrest of Meiosis in Female Animals.- 7. Meiotic Variation Controlled by Genetic Differences.- a) Genotypic Control of Meiosis.- b) Position Effects at Meiosis.- 8. The Effects of the Environment on Meiosis.- VI. The Regulation of Meiosis.- Codetta.- References.- Species Index.- Author Index.

Introduction When the study of heredity and variation first came to be treated as a scientific subject-and this, one must remember, was only just over a hundred years ago-there was an unfortunate separation between the disciplines of cytology and experimental breeding. This separation was based partly on a lack of understanding and partly on a lack of the desire to understand. Even WILLIAM BATESON, the first apostle of mendelism in England, had a blind spot for cytology and for many years dogmatically refused to believe that MENDEL'S determinants were transmitted and distributed by the chromosomes. This separation between cytology and experimental breeding is one which persists, in a measure, even today, simply because there are two quite different, though complementary, techniques available for the study of heredity and variation. On the one hand, one can study directly the structure and behaviour of the actual vehicles which transmit the genetic determinants from one generation to the next. This is the method employed by those who study genetics through a microscope. The alternative method is that used by the experimental breeder who, in default of being able to watch the hereditary factors segregate from each other directly, is obliged to examine the constitution of the germ cells indirectly by sampling, and usually at random, the products of a controlled mating.