18 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 



the extra Houdan toes are I', I", and those of the reduced Silkie are V'a 

 and I"h. Finally, in Silkies, the inner toe (I') may spht (more or less com- 

 pletely), and thus the 7-toed condition arises. Moreover, in Houdans I 

 have on one or two occasions found the lateral element (I") bifid distaUy, 

 resembling perfectly the typical condition found in the Silkies. 



A simple nomenclature is suggested for these various types of extra- 

 toes. The simple double-toed condition, as found commonly in Houdans, 

 may be called the duplex type (D). The loss of I' gives the reduced duplex 

 (D')- The case of split I", as commonly seen in the Silkie, is the triplex 

 type (T) ; with the loss of I' this becomes the reduced triplex (T', not duplex!). 

 The 7-toed condition of Silkies may be called the quadruplex type (Q); 

 the combination split I' and single I" gives the reduced quadruplex (Q0-* 



The reduction that leads to the loss of I' consists of a loss of phalanges, 

 as Bateson (1904) has already pointed out. It seems probable that the 

 reduction affects first the proximal phalanges, since the distal nail-bearing 

 phalanx is the last to disappear. 



B. RESULTS OF HYBRIDIZATION. 



First let us consider the result of mating extra-toed individuals belong- 

 ing to "pure" extra-toed races. A typical Houdan cock (D type), of the 

 well-known Petersen strain, was mated with 3 hens bred by me, but derived, 

 several generations before, from the same strain. With the first hen he got 

 29 chicks, all with the extra-toe except one (3.3 per cent) that had 4 toes on 

 both feet and two that had 4 toes on one foot and 5 on the other, i. e., one foot 

 simplex and one duplex. With the second he got 12 chicks, of which one 

 had 4r-5 (D) toes. The third, in 26 young, gave one with 4 toes on each foot. 

 Thus, in 67 chicks altogether there were 2, or 3 per cent, with the normal 

 number of toes on both feet (4-4). Unfortunately these birds did not 

 survive, so it is not known whether they would have thrown as large a 

 proportion of extra-toed offspring as 5-toed Houdans. Bateson's Dorkings 

 gave about 4 per cent of 4-toed offspring. Of the 83 offspring of 6-toed 

 Silkies, 3, or 3.6 per cent, had 4 toes on each foot. Even in pure-bred poly- 

 dactyl races, consequently, the character "extra-toe" does not uniformly 

 appear in the offspring. 



Let us consider next what happens when a polydactyl individual is 

 crossed with a normal individual. Table 10 gives the results of all matings 

 of this sort and its most obvious result is that the polydactyl condition 

 reappears in every family, but not, as in typically Mendehan cases, in all 

 of the offspring; at least this is true of the Houdan crosses. In the Silkie 

 crosses the 6 offspring given as having the single thumb may possibly have 

 been of the type D', as that type was not in mind at the time of making the 

 record and was not always distinguished from type S. It is also clear that 

 the offspring of Silkie crosses are more apt to be polydactyl than those of 



* E. 0., Pen 813, 935 9, embryo from egg of May 13. 



