1. Zeuthen, E., Pub. Staz. Zool. Napoli, 23 supp., 47 (1951).
2. Agrell, I., C.R. Soc. Biol., 149, 1754 (1955).
3. Hoff-Jorgensen, E., and Zeuthen, E., Nature, 169, 245 (1952).
4. Hoff-Jorgensen, E., “Rec. Develop. Cell. Physiol.”, 79 (London, 1954).
5. Lindh, N., Ark. f. Zool., ser. 2, 9, 426 (1956).