Exencephaly in chicken-pheasant hybrids.

1. The incidence of exencephaly was investigated in chicken-pheasant hybrids. 2. With the pheasant as sire, fertility was 7-6%, but with the fowl it was 19-5%; hatchability of fertile eggs, however, was similar, 42% and 41% respectivley. 3. Only one exencephalic hybrid was obtained when the sire was the pheasant but 70 were noted when the fowl was sire. The incidence of this malformation in hatched chicks was 12 times more in crosses with the fowl as sire than in the reverse cross. 4. The frequency of exencephaly was greater with Rhode Island Red, Barred Leghorn or White Leghorn roosters than with Columbian Rock roosters.