SYNDACTYLISM. 33 



throw, even in large families, 100 per cent syndactyl offspring. But only 

 2 families, Nos. 30 and 34, have yielded 100 per cent syndactyls, and these 

 contained 2 and 1 offspring, respectively; so they are not significant. 

 On the other hand, there are numerous matings of 2 extracted normal- 

 toed parents that have produced only normal-toed offspring (families Nos. 

 14, 15, 21, 22, 23, including 119 individuals). Consequently the conclusion is 

 favored that normal-foot is recessive and syndactyl-foot dominant, and 

 this shall be our working hypothesis. 



On our hjrpothesis. No. 121 is probably a heterozygote. Mated with 

 the recessive normal, expectation is 50 per cent heterozygous, showing 

 sjoidactylism; the remainder normal- toed. But dominance is here, as in 

 polydactylism, very imperfect. For this reason and because it was not 

 looked for, no syndactylism was noted in the first hybrid generation. The 

 offspring prove to be of two sorts, however. No. 180 c? is a pure recessive, 

 and in 8 matings with as many different sisters of his he got 184 normal- 

 toed to 1 syndactyl. These same sisters, mated to another brother, No. 

 242, in some cases gave 9 per cent and 10 per cent syndactyl. No. 242 is, 

 consequently, probably a DR and, mated to DR sisters (which constitute 

 according to expectation about one-half of all) gives some DD's, part of 

 which constitute the 9 to 10 per cent of sjoidactyls. Of course, 25 per cent 

 DD is to be expected; the difference gives a measure in this instance of the 

 imperfection of dominance in the "extracted" as well as "heterozygous" 

 condition. 



Matings 9 to 15 (pen 747) are instructive in comparison with the fore- 

 going case. Both parents are derived from pen 658, which contained as 

 breeders a heterozygous Dark Brahma male (No. 146) and various females 

 of non-booted races far removed from suspicion of syndactylism; expecta- 

 tion being an equal number of DR and RR offspring. In pen 747 No. 1888 c? 

 acts Hke a DR, and so do the hens in matings 9 to 13, while the hens in the 

 other 2 matings are doubtless RR's. The former give 17 per cent syndactyl 

 offspring, the latter none at all (in 56 individuals). 



Matings 16 and 17 (pen 703) are between pure-bred Dark Brahmas that 

 are probably DR's. About 22 per cent of their offspring are sjoidactyl — 

 a rather higher proportion than we have found before. Matings 18 to 19 

 are between progeny of pen 627. In mating 20 the normals were not 

 recorded. The cock in this pen. No. 871, is probably heterozygous, as are 

 also the first two hens, so that nearly 30 per cent of their progeny are syn- 

 dactyl. From the other 3 hens no syndactyl offspring were obtained. Evi- 

 dently the two sets of hens have a very different gametic constitution. 

 The existence of two sorts of families is one of the strong arguments for 

 the segregation of this character. 



We next come to the pens (matings Nos. 24 to 42) which were especially 

 mated to study the inheritance of syndactylism. I had now, for the first 

 time, two parents with syndactyUc feet. 



