STUDIES ON THE CELLS OF CATTLE WITH SPECIAL REFERENCE TO SPERMATOGENESIS, OÖGONIA, AND SEX-DETERMINATION

Abstract

1. Thirty-seven chromosomes occur in the spermatogonia. One, the sex-chromosome, is distinctly larger than the others.2. Nineteen chromosomes appear in the primary spermatocyte division, of which eighteen are bivalent and the other is the unpaired sex-chromosome.3. In the primary spermatocyte division the heart-shaped sex-chromosome passes undivided to one pole in advance of the other chromosomes.4. The primary spermatocyte division is evidently the reduction division, giving rise to two different types of secondary spermatocytes, one with the sex-chromosome and the other lacking it.5. The one type of secondary spermatocyte, which contains the sex-chromosome, gives rise to two spermatids, each containing the sex-chromosome and eighteen ordinary chromosomes.6. The other type of secondary spermatocyte, which lacks the sex-chromosome, gives rise to two spermatids, each containing only the eighteen ordinary chromosomes.7. The mature spermatozoa are of two types, equal in numbers. The one type is larger and contains the sex-chromosome. The smaller type is without the sex-chromosome. The larger type is female producing, while the smaller is male producing.8. Thirty-eight chromosomes occur in the oögonia; two of these are the sex-chromosomes.9. The reduced number of chromosomes in the female is, in all probability, eighteen ordinary chromosomes and one sex-chromosome which apparently occurs in all of the mature ova.10. The somatic cells of the male contain thirty-six ordinary chromosomes and one sex-chromosome.11. The somatic cells of the female contain thirty-six ordinary chromosomes and two sex-chromosomes.12. The number of chromosomes in the somatic cells of the two sexes is in exact accord with expectations.13. There is no relation between the time in the heat period at which the cow is served and the sex of the offspring.14. Sex in cattle, for the present, remains a matter beyond the control of the breeder. It is determined by the sex-chromosomes; it is a matter of inheritance.15. Sex-limited inheritance strengthens the belief in the chromosome theory of sex-determination.