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23 chromosomes accessory chromosome anaphase Aphrophora appears bivalent chromosomes body bouquet stage centrosome chro chromatin chromatin element chromo classes closely component condensed connected conspicuous containing corresponding crosses cytoplasm daughter plates deeply described disappears divides division double early elongated equatorial plate evidently Family favorable female fertilization fiber followed granules growth stage Hemiptera heterochromosome insects iron-hæmatoxylin large chromosomes larger late later stage Lepidoptera longitudinal split loops male mass material maturation division maturation mitosis maturation spindle metakinesis metaphase mosomes nucleus occur odd chromosome Orthoptera plasmosome plate of spermatogonium polar present prophase pupa remains respectively second maturation Second spermatocyte seems seen segments separated sex determination showing shown in figures side Similar stage small chromosome smaller somatic cells species spermatids spermatogenesis spermatogonial mitosis spermatogonium spermatozoa spindle spireme stage stage fig staining suggests synapsis stage telophase tetrads unequal pair usually various young
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 20 - 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