1905.] HEREDITY IX PIGEOXS. 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 ocsur in the 

 offspring of normal-footed pirents, 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 ta 

 time in the same strain, birds showing the charactar having 

 been discarded. 



The general result of the exj)eriments 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 

 vi-ith, 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 occa- 

 sionally, 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 witli 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-footed S used in Experwients. 



The Pigeon which I used in the following expeiiments 

 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 sufliciently 

 loose to allow the usual spread of the foot. The bird was of the 



Proc. Zool. Soc — 1905, Yol. II. No. XXXYII. 37 



