ON THE CYTOLOGY OF TITYUS BAHIENSIS WITH SPECIAL REFERENCE TO MEIOTIC PROPHASE

Abstract

of chromosomes from related species described by other authors, as first stated by PIZA (1939a). Somatic divisions show six irregularly curved chromosomes: in the meiosis of spermatocytes three tetrads are easily distinguished, all chromatids being rod shaped, without showing signs of chiasmas, of constrictions, or any specific attachment region. The most interesting feature so far reported is the parallel movement of the chromosomes or chromatid pairs during the first anaphase. This parallel movement in Tityus seems to be the same as described first by SCHRADER (1935) for some Hemiptera (see GEITLER 1938 for further references). PIZA (1939b) has formulated far reaching speculations on this subject with which we cannot agree. The description of meiotic prophase as given by PIZA (1939a) is very incomplete. He describes very briefly leptotene, zygotene, and early pachytene stages, without corresponding illustrations. I n the description of pachynema PIZA (1939”~ p. 256) writes that “the nucleus seems to be occupied by extensive filaments of very clear chromomeric structure which describe many and large spirals, strongly accentuated in the point of separation of the respective segments.” It is not clear to what structure the term “segment” refers. Later prophase stages were not observed in the three males studied by PIZA. He assumes that in late pachynema the tetrads condense and become regular in outline, passing thus into metaphase (fig. 3, Z.C.). Finally PIZA declares categorically that “nothing exists which could be compared to a true chiasma” (Z.C., p. 2 5 7 ) . Here again we encounter some difficulty in interpreting the statement without a clear definition of what the author calls a “true chiasma” (quiasma verdadeiro). Figures d and f (plate I , Z.c,), which show photomicrographs of a chromosome arrangement in metaphase with a reciprocal translocation, are described as “chiasmas between two bivalents caused by reciprocal translocations.” We could not find any further observations on the prophase in the later papers (PIZA 1939b, 1940, 1941). The first difficulty in our study of this animal consisted in the relatively small number of males to be encountered. In several localities no male was found a t all among several hundreds of females, and it has not yet been possible to decide about the method of reproduction in these cases. In other localities, all in the vicinity of the same town, males were found, though always in smaller number than females. Small individuals have generally very few cells in meiotic T Sgo Paulo, Brazil, differs considerably with regard to form and number