Abstract
The fertilization phenomena in Hynobius retardatus are observed in sections of the eggs, fixed at different intervals after insemination of the spermatozoa. The results are briefly outlined as below:
1) About 1 to 1 1/2 hours after insemination of the spermatozoon the the second polar division is completed, and formation of the second polocyte follows about 1 1/2 to 2 hours after insemination.
2) About 2 1/2 to 3 hours after insemination there is found at the periphery of the egg the already metamorphosed female pronucleus, which moves away from the surface towards the interior of the egg.
3) The spermatozoon enters the egg as early as 15 minutes after insemination and then, within 1 hour, it metamorphoses into the male pronucleus.
4) The conjugation of the male and female pronuclei generally takes place between the 5th and 6th hour after fertilization. They meet at a distance of about 1/4 to 1/3 the egg diameter from the animal pole, along an egg-axis joining the second polocyte with the center of the egg.
5) At the time of the conjugation, both pronuclei are quite similar in their structure, size and staining condition; they are nearly spherical with a smooth nuclear membrane and are filled with colourless nuclear sap. Generally they measure 0.038-0.042mm in diameter.
6) After the two pronuclei meet together, they do not actually fuse, but lie side by side in close contact with the nuclear membrane intact. The maternal and paternal nuclear elements are separated in distinct groups during the stages preparatory to the first cleavage division and the chromosomes are formed independently in each respective nuclear vesicle.
7) In the egg about 7 hours after insemination, the first cleavage spindle is usually found in the process of division.
