THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM (HOMOPTERA)

Abstract

1. The chromosome number in all male diploid groups of Cicada (Tibicen) septemdecim is 19, and in the female diploid groups 20.2. The diploid chromosome groups are characterized by the presence of one large pair of chromosomes (the macrochromosome pair, AA) and two pairs of somewhat smaller chromosomes (BB, CC). The other 13 chromosomes show no size differences.3. There is no variation in chromosome number or in their form and arrangement in any of the diploid groups studied.4. In the spermatocytes there are two ring tetrads of the Stenobothrus type, which are derived from the AA and BB chromosome pairs of the spermatogonia. These tetrads divide reductionally in the first maturation division.5. An odd chromosome is present which persists as a nucleolus in the growth stages of the spermatocyte. It passes undivided to one pole in the first maturation division and divides in the second division.6. The tetrads are always grouped characteristically in the metaphase of the first maturation division and the same grouping is found in the metaphase of the second spermatocytes.7. The synaptic stages in the oöcyte were studied, giving evidence that the chromosomes pair side-to-side (parasynapsis).8. Two chromatin nucleoli are present in the preleptotene stages of the oöcyte. These disappear in the synaptic stages and reappear in the post-synaptic stages. These nucleoli are interpreted to represent the two sex-chromosomes of the female which go through a synaptic phase like the autosomes.9. Mitochondria are found in the spermatogonia in the form of granules localized at the end of the cell bordering on the cyst cavity.10. The first evidences of a degeneration of a spermatogonium is shown by an agglutination of the mitochondria. As degeneration continues the mitochondria continue to agglutinate forming large lipoid globules in the cell, evidently yielding a fatty degeneration.11. In the spermatocytes the mitochondria are filar; they surround the spindle peripherally at the time of the maturation divisions and become divided by the cell-constriction. The mitochondria of the spermatid form the round compact Nebenkern which later becomes drawn out as a sheath surrounding the axial filament of the spermatozoon.12. The ovaries of Cicada are typically Hemipteran in structure. The egg-strings of the oöcytes pass up into the nurse chamber and serve to carry the nutrient materials to the oöcytes. In the ovaries of the adult, the nurse-cells are ingested at the upper end of the egg-string and their ingested products pass down into the oöcyte as nutrient materials.13. Mitochondria are found in the young oöcytes as a deeply staining mass of granules lying in the cytoplasm at one pole of the nucleus. In the later stages the mitochondria gradually extend around the nucleus forming a peninuclear zone of mitochondria.14. The mitochondria increase greatly in numbers during the postsynaptic stages still retaining their perinuclear arrangement.15. When the cytoplasmic volume of the oöcyte has reached its maximum, the perinuclear arrangement of the mitochondria becomes lost and the mitochondria become dispersed toward the periphery of the oöcyte.16. At the periphery of the oöcyte, the mitochondria become transformed into yolk-spherules. First vacuoles are found surrounding the mitochondria, these structures resembling the "pseudo-nuclei" of Blochmann. The substance of the vacuoles at first takes the plasma stain lightly and as it grows in size, it becomes more and more deeply staining. The globules increase greatly in size and show a marked affinity for the basic stains.17. The relation between the perinuclear zone of mitochondria and such structures as yolk-nuclei, etc., is pointed out.18. The zone of the cytoplasm immediately surrounding the nucleus is taken to be the locus in the cell of the formation of mitochondria through the chemical action of the nucleus upon the products of assimilation taken in by the cytoplasm.