抄録
A heteromorphic bivalent, having one terminally and one medianly attached chromosome, always segregates reductionally in the first meiotic division.
Two heteromorphic bivalents, with sub-median attachments an each chromosome sometimes separate equationally in the first division.
The spindle attachment is shown to remain unchanged, and the possibility that non-sister chromatids may be associated at the spindle attachment is not in accord with these observations. The hypothesis that sister chromatids are associated at the spindle attachment and that equational first divisions are due to crossing over is in full accord with the observations.
