THE MEIOTIC CHROMOSOMES OF THE MALE LLAVEIELLA TAENECHINA MORRISON (COCCIDAE) AND THE QUESTION OF THE TERTIARY SPLIT

¹ From the Department of Zoölogy, Columbia University

1. The diploid chromosome set of the female Llaveiella taenechina comprises three pairs of rod-shaped chromosomes distinguishable by size. The shortest one is unpair in the male, giving a diploid set of 5.

2. The chromosome behavior and achromatic figure are normal in the female cycle and in the male somatic and spermatogonial mitosis. Meiosis in the male conforms to the Llaveia type, but only a minority of the spermatocytes adhere strictly to this scheme. The majority of the cells show different combinations of four major types of variation, all of which are successful in sperm formation. The variant procedures may be summarized as follows.

(a) Chromatid autonomy. The chromosomes are subdivided along the tertiary split. Each pair of half chromatids produces an individual spindle. Anaphasic movements may start at different times and proceed at different rates in the four chromatid spindles. In the second anaphase the two chromatid spindles of an autosomal group may fuse to form a linear aggregate of chromosomal elements in single tubular spindle.

(b) The complete dissociation of chromatids. The two chromatids of the X chromosome may evolve in separate prophase vesicles and divide independently of each other in the first division. The re-association of their derivatives and their common passage to one pole in the second division is not thereby affected.

(c) Asynapsis. Each member of one or both pairs of autosomes may evolve in a separate prophase vesicle, without synapsis and chiasma formation, produce an individual spindle, and divide independently of its mate in the first division. Chromosome pairing for the second division is not thereby affected.

(d) Quarternary split. Occasionally one or more chromosomes may be further subdivided along the fourth or quarternary split.