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Show A discrepancy will be noticed between the numbers of birds illustrating the foot character and those which show presence or absence of " shell" in the same experiment. Ibis is accounted for by the fact that it is possible to recognise the webbed 01 normal foot on hatching, or even in birds found dead in the eggshell if sufficiently incubated, whereas the presence or absence of the " shell " can only be ascertained when the feathering of the young birds is fairly advanced. It was noticed that many of the young birds which were webbed were extremely weakly in the nest, and several of them died at a very early age. Of the three extracted web-footed birds bred in Exp. 4 from the D R xD R mating, not one was reared. The extracted webbed birds whose purity was tested were all bred from the DR x R matings. Discussion of Results. Foot character.-It will be seen from the foregoing table that the feet of the F. 1 generation, of which six birds were bred, were all normal, the web character behaving as a recessive. Two pairs of F. 1 were mated, and in experiment 4 the webbed foot reappears in three birds out of the twelve, this being the exact proportion expected on the Mendelian hypothesis. From the other pair (Exp. No. 3), however, no recessives appeared, and the mating was repeated in 1904, as Exp. 6, with the same result. During the two years that these birds were mated together 29 eggs were laid and 23 birds produced, all showing the normal foot character. The absence of webbed birds in this family was quite contrary to expectation, for 5 or 6 recessives were to be expected. In order to test the matter further, in 1905 the two F. 1 birds in question were mated to extracted recessives, and, as will be seen on referring to experiments 1 1 and 1 2 , webbed and normal offspring were then obtained in approximately equal numbers in accordance with Mendelian expectations. The absence of recessives in the 23 birds in F. 2, bred in experiments 3 and 6, is very remarkable. Whether it arose from any definite disturbing cause, or was merely a chance aberration, cannot be asserted. The behaviour of the same birds when mated to pure R clearly proves that their gametic production was then normal. In the matings of DR's both with the original recessive web and with the extracted recessives the results are simple. It will be noticed that in ' experiments 2, 5, 11, and 12 fifteen webbed and fifteen normal birds were produced, the Mendelian expectation of such a mating being equality. It being impossible to test the purity of wrebs bred by the DR x DR matings, as the birds died in the nest, the extracted recessives from the DR x R matings were used, and experiments 7, 8, 13, and 14 show the results. Nineteen birds were raised in these four experiments, all having the feet webbed. 554 MR. R. STAPLES-BROWNE ON ■ [Dec. 12, |