OCR Text |
Show 1905.] HEREDITY 1ST PIGEONS. 551 only on each foot, and it is more usual to find the development of the web nearly symmetrical in the two feet. It sometimes occurs between digits ii. and iii. sometimes between iii. and iv., and sometimes between all three. The instances in which it reaches the bases of the claws between all the digits on both feet are rarer. It has occurred on one foot only. Though this character has been observed to occur in the offspring of normal-footed parents, I have never heard of an instance in which all the young so bred were webbed. It has been found in a pigeon bred from parents of two different strains, and I have also heard of cases in which it occurred from time to time in the same strain, birds showing the character having-been discarded. The general result of tli3 experiments is that the inheritance of the webbed foot is Mendelian. It is recessive to the normal foot. The character is not a thoroughly satisfactory one to work with, as it is liable to considerable fluctuation in extent. Extracted recessives, though all show webbing, have this character in various degrees; in some it reached only to the first interphalangeal joint of the second and third digits, or to the second joint of the fourth digit. On examining the normal population 1 find that birds occasionally, though rarely, occur with webs as extensive as this. In the families here recorded I took the first interphalangeal joint of the second and third digits and the second joint of the fourth digit as a minimum, and counted as " webbed" all birds with a web reaching this minimum in the case of at least two adjoining digits : all birds with less webbing than this being given as normal. If a much greater series of numbers could be investigated, undoubtedly there would be overlapping between the two classes of normal and webbed birds. On the other hand, the evidence, so far as it goes, does not indicate that the degree of webbing in the parents closely limits the amount in the offspring, for moderately webbed birds have given birds more webbed, and fully webbed birds have given offspring less webbed (see exp. 13 and 14). I hope later to make further experiments with the lower states of this condition. Web-footecl 3 used in Experiments. The Pigeon which I used in the following experiments somewhat resembled an Antwerp in appearance, but was of no distinct variety. The web extended to the base of the claws in both feet, but the digits were rather closely webbed together except iii. and iv. of the right foot, where the web was sufficiently loose to allow the usual spread of the foot. The bird was of the P roc. Z ool. Soc.-1905, V ol. II. No. XXXVII. 37 |