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19 chromosomes 19 large accessory chromosome acrosome anaphase Aphrophora quadrangularis appears archoplasmic bivalent bivalent chromosomes Blattella germanica bouquet stage centrosome chro chromatin element chromatin nucleolus chromo Chrysomelida Coccinellida Coleoptera cysts daughter plates divides elongated equal pair equatorial plate Family Chrysomelida germ cells growth stages figs Hemiptera Hemiptera heteroptera Hemiptera homoptera hetero heterochromosome group heterochromosome pair idiochromosomes large chromosomes larger later stage Lepidoptera linin longitudinal split loops m-chromosomes maturation division maturation spindle metaphase mosomes nuclear membrane odd chromosome oöcytes oögonia Orthoptera pair of chromosomes pair of heterochromosomes plate of spermatogonium polar plates prophase rest stage safranin-gentian preparation Sagitta Second spermatocyte segments sex characters sex determination showing the heterochromosome shown in figures Similar stage small chromosome somatic cells species of Coleoptera sperm sperm-head spermatids Spermatids containing spermato spermatogenesis spermatozoa spindle figs spindle-remains spireme stage Stenopelmatus STEVENS synapsis stage synizesis stage telophase Tenebrio molitor tetrads Trirhabda unequal pair Young spermatid
Página 18 - indicate that sex may in some cases be determined by a difference in the amount or quality of the chromatin in different spermatozoa. This is much the most suggestive part of the work, and it will be followed up by the study of related forms. There appears to be so little uniformity as to the presence of the
Página 3 - STUDIES IN SPERMATOGENESIS WITH ESPECIAL REFERENCE TO THE "ACCESSORY CHROMOSOME." By NM STEVENS. In connection with the problem of sex determination it has seemed necessary to investigate further the so-called "accessory chromosome," which, according to McClung ('02), may be a sex determinant. This view has been supported by Sutton ('02) in his work on
Página 18 - chromosomes of equal size must produce a female. The small chromosome itself may not be a sex determinant, but the conditions in Tenebria indicate that sex may in some cases be determined by a difference in the amount or quality of the chromatin in different spermatozoa.
Página 18 - even in insects, and in their behavior when present, that further discussion of their probable function must be deferred until the spermatogenesis of many more forms has been carefully worked out. BRYN MAWR COLLEGE, May
Página 16 - maturation mitoses. The whole history of this element suggests that it may be rejected chromatin analogous to that observed in the ovogénesis of many forms. In
Página 18 - large ones. Since the male somatic cells have 19 large and i small chromosome, while the female somatic cells have 20 large ones, it seems certain that an egg fertilized by a spermatozoon which contains the small chromosome must produce a male, while one fertilized by a spermatozoon containing
Página 15 - 03), nor has any been detected in connection with fertilization. It is certain that none is present in the first segmentation spindle of the egg. GENERAL DISCUSSION. THE "ACCESSORY CHROMOSOME." The literature bearing on the ' ' accessory chromosome ' ' of McClung, the ' ' small chromosomes '
Página 12 - Coarser spireme stage. 101-103. Bouquet stage. 104-105. Later spireme stage. 106. Various forms assumed by the combined nucleolus and element x; last figure from a giant cell. 107. Segmenting spireme. 108. Similar stage to fig. 107, one chromosome longitudinally split; element x
Página 18 - in the sperm nucleus in the egg, or in the first segmentation spindle. Its function must, therefore, be confined to the process of spermatogenesis. From the standpoint of sex determination, we