Quarterly Journal of Microscopical Science, Vol s2-77, 585-604, Copyright © 1935 by Company of Biologists

Memoirs: The Germ-Cell Cycle in Phytophaga destructor Say

¹ Zoological Department of the Johns Hopkins University, Baltimore

1. The somatic cells in both sexes of Phytophaga destructor Say contain four pairs of V-shaped chromosomes, the sex-group being indistinguishable in size or form.

2. The germ-cells in both sexes contain eight pairs of chromosomes.

3. The maturation of the egg follows the normal course of development, eight bivalents being formed. After polar body formation the female pronucleus has eight chromosomes. The polar bodies are never extruded from the egg.

4. Spermatogenesis is a complicated process, the details of which have not been satisfactorily determined. The growth stage appears to take place before the last spermatogonial division. No pairing of chromosome has been observed, and apparently no metaphase plate is formed at meiosis. Eeduction is effected by the expulsion of two buds each containing four chromosomes. Thus only one sperm is produced from each spermatocyte.

5. One or more sperms may enter the egg at fertilization.

6. The germ-line is differentiated from the soma at the eightcell stage.

7. At the fifth cleavage the somatic nuclei eliminate half their number of chromosomes, and are left with eight chromosomes.

8. Migration of the germ nuclei takes place at the sixteencell stage.

9. The relation of the chromosome numbers in the somatic and germ lines is discussed.