In a series of papers it has been shown thatTityuschromosomes are provided with one centromere at each end (2, 4, 5 and 6). Proofs of such a view were found in the behaviour of the chromosomes in the course of spermatogenesis in the widely distributed Brasilian speciesT. bahiensis(Perty). Indeed, the long rod-shaped bivalents of this interesting species orient themselves in such a way that, while their bodies lie flat in the equatorial plane, the partners' corresponding ends are turned towards opposite poles. Metaphase side views show that the paired chromosomes are separated throughout their length. Being entirely unconnected by chiasmata, the chromosomes move toward the poles in perfect parallel, with the ends forward until late anaphase, when they bend strongly. Fragments bearing a single terminal centromere perform anaphase movement parallel to the spindle axis, as do the orthodox acrocentric rod-shaped chromosomes (11).