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Show 556 MR. R. STAPLES-BROWNE ON [Dec. 12, Variation in the Amount of Webbing. I have stated that the webbed foot is subject to considerable fluctuation, both when the character is observed to occur in normal strains and when it appears as an extracted recessive in these experiments. Table II. is arranged to show the approximate stretch of the web in the case of each bird recorded in the experiments. The observations were made by bending the foot and noting to which part of each digit the web was attached. In the table D stands for the digit, and <j> for the phalanx. Unless otherwise stated, it should be understood that the web is attached to the distal end of the phalanx in question ; but if a fraction is inserted after the number of the phalanx, then the web is attached halfway or three-quarters of the way up that phalanx. No very accurate means of measurement were applicable, and the estimations should be taken as approximate only. The experiment numbers refer to Table I. Brackets are placed round the number of a bird to signify that the bird died either in the egg-shell or very soon after hatching. In all 37 web-footed Pigeons have been raised in the experiments, but upon such small numbers discussion of the relationship of the several graduations is impossible. It may, however, be noted that some extremely small webs were raised in experiments 7 and 8, although the birds were bred from parents both showing the web character in a higher degree. Experiments 13 and 14 have already been discussed. II. T h e S h e l l . It will be seen from Table I. that this character behaves as a simple recessive throughout the experiments with the webbed strain (but v. infra). In experiments 3, 4, and 6, out of the 29 birds bred, 6 show the " shell" in F. 2, a sufficiently close result. The extracted recessives hied true, as shown in Exp. 9. In Exp. 10 the number of recessives (5 : 2) is too high for a DR X R mating, which should have given equality, but the total is very small. Farther Experiments with " Shell." . The same Nun female which was used in the foregoing experiments was also mated to a Barb male. There is no need to give here a description of the Barb beyond the statement that the feathers on the head are always smooth and no crest or " shell " is ever found. The results of the mating of Barb 3 and Nun $ are recorded in Table III. |