1. Abt, D. A., Crowshaw, J. E., Hare, W. C. D.: Monocephalus dipygus parasiticus and other anomalies in a calf. J. Amer. vet. med. Ass. 141, 1068–1072 (1962).
2. Ainsworth, L., Ryan, K. J.: Steroid hormone transformations by endocrine organs from pregnant mammals. I. Estrogen biosynthesis by mammalian placental preparations in vitro. Endocrinology 79, 875–883 (1966).
3. Alexander, G., Williams, D.: Ovine freemartins. Nature (Lond.) 201, 1296–1298 (1964).
4. Anderson, D., Billingham, R. E., Lampkin, G. H., Medawar, P. B.: The use of skin grafting to distinguish between monozygotic and dizygotic twins in cattle. Heredity 5, 379–397 (1961).
5. Aronson, S.: A case of transplacental tumor metastasis. Acta paediat. (Uppsala) 52, 123–124 (1963).