1. A. A. Voitkevich, Dokl. AN SSSR,135, 1 (1960) p. 221.
2. A. A. Voitkevich, E. I. Zubkova, and I. I. Grigor'ev, Dokl. AN SSSR,130, 4 (1960) p. 940.
3. L. B. Levinson, Proceedings of the 5th All-Union Congress of Anatomists, Histologists and Embryologists [in Russian] (Leningrad, 1951) p. 410.
4. A. L. Polenov, Uchen. Zapiski Leningradsk. Med. Inst.,3 (1959) p. 176.
5. J. Barry, C. R. Soc. Biol.,152 (1958) p. 809.