NUMBER AND BEHAVIOR OF THE CHROMOSOMES INCAVIA COBAYA(THE COMMON GUINEA PIG)

Abstract

1. The actively dividing cells are not distributed throughout the whole lining of the seminiferous tubules but are limited to elliptical areas. 2. These areas never exceed two thirds the circumference of the tubules and sometimes consist of only a few cells. 3. The greatest diameter of the ellipse is always lengthwise of the tubule. 4. The areas of actively dividing cells are more numerous and larger in the superactive male. 5. There are thirty-eight spermatogonial chromosomes, which according to size and shape may be grouped into eighteen similar pairs and a pair which is unequal in size which we have designated as the XY-pair. 6. Both the primary and secondary spermatocyte cells have nineteen chromosomes. 7. The XY-tetrad is precocious in its division and the resultant chromosomes are unequal in size. 8. All the chromosomes divide equally in the second division. 9. There is some evidence of parasynapsis.