554 ME. R. STAPLES-BROWXE ON [DeC. 12, 



A discrepancy will be noticed between the numbers of birds 

 illustrnting the" foot character and those which show presence or 

 absence of " shell " in the same experiment. This is accounted 

 for by the fact that it is possible to recognise the webbed or 

 normal foot on hatching, or even in birds found dead in the egg- 

 shell 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 DR X DR 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 11 and 

 12, webbed and normal offspring were then obtained in approxi- 

 mately equal numbers in accordance with Mendelian exj^ectations. 



The absence of recessives in the 23 birds in F. 2. bred in 

 experiments 3 and 6, is veiy 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 i-ecessive web 

 and with the extracted recefsives 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 webs bred by the 

 DR X r)R matings, as the birds died in the nest, the extracted 

 recessives from tlie DR x R matings wei'e used, and experiments 

 7, 8, 13, and 14 show the results. Nineteen birds were raised in 

 tliese four experiments, all having the feet webbed. 



