On maturation in the eggs of Limnaea stagnalis L

1. The maturation divisions of the egg of Limnaea stagnalis L. have been studied. 2. The haploid number of chromosomes is 18. 3. At the telophase of the first maturation division, the central group of dyads reaches the surface of the inner central body of the first maturation amphiaster. 4. This central body directly transforms into the second maturation spindle. 5. The aster surrounding this central body gradually disappears. New astral radiations are formed in the cytoplasm near the outer end of the newly formed second maturation spindle. 6. The spermaster, which appears during the telophase of the first maturation division, fuses secondarily with the inner end of the second maturation spindle and forms the inner aster of the second maturation amphiaster. 7. After the extrusion of the second polar body, this aster shifts to a deeper position near the centre of the egg, where it remains visible for some time, but ultimately disappears. 8. The egg chromosomes swell into karyomeres immediately after the extrusion of the second polar body. At the same time, the sperm nucleus begins its migration towards the animal pole.