100 Cc. H. DANFORTH 
The living embryos were fixed in Zenker’s fluid or in 10 per 
cent formalin. They were subsequently examined under a 
binocular microscope and parts of many of them were either 
sectioned or stained by the van Wijhe method and studied in toto. 
The contents of eggs found to contain dead chicks were put 
in formalin and after a short period of hardening the embryos 
were examined, their age estimated and characteristics recorded. 
All the toes on both feet of each of the 86 living chicks were 
measured, the grade of polydactyly, the grade of booting and 
also the form of the comb were noted. These data likewise 
were recorded so far as possible for the older embryos. For 
each of the living chicks an index of brachydactyly was obtained 
by dividing the sum of the lengths of the two lateral toes (digits 
IV) by the sum of the lengths of the two medial toes (digits II). 
This gives a value varying above and below 1. The value 
obtained is multiplied by 100 in each case to eliminate fractions. 
The index is thought to be fairly reliable, since careful measure- 
ments have shown that the fourth toe is the one chiefly affected 
while the third is only slightly so and the second possibly not at 
all. The toe measurements represent the distance, obtained by 
the use of dividers, from the base of the nail to the metatarso- 
phalangeal articulation. 
DESCRIPTION OF STOCK USED FOR BREEDING 
The females employed in the breeding experiment were all pure 
bred white Leghorns of a well established strain. Their shanks 
were free from feathers and there was no indication of poly- 
dactyly or brachydactyly. The fourth toe index ranged from 
106 to 121 with an average of 112. All were pure white with 
large single combs. Eight of these and a male were obtained 
in 1916 from a poultryman who devotes himself exclusively to 
this breed. The other five were raised at the laboratory from 
this original flock. There can be little doubt as to the purity 
of the stock especially in regard to the characteristics under 
investigation. At the time of the experiment five of the hens 
were less than ten months old, the rest were two years or more. 
