108 Cc. H. DANFORTH 
the most stable, the intermediate elements being the ones first 
affected. 
The fourth degree was found in no. 12 (half brother of these 
chicks), referred to at the beginning of the paper, and in several 
chicks obtained later. Here there are only two bones present 
in the fourth toe (fig. 1, B). There is no nail. The tendon of 
the flexor profundus is inserted on the plantar surface of the 
terminal bone and the superficial flexér into the lateral aspects 
of both segments. In view of this arrangement, the conforma- 
tion of the two bones, and the condition observed in other 
specimens it would seem probable that the proximal element 
represent the normal basal phalanx while the distal one repre- 
sents a fusion (in effect, if not in reality) of phalanges II, III 
and IV; phalanx V being entirely absent. 
Owing to the brief period between the first indication of 
clearly demonstrable brachydactyly and the appearance of 
phalangeal cartilages, the possibility that the precartilage cells 
are the ones first affected by the shortening factor can not be 
entirely excluded. If such be the case, it is the skeletal elements 
that from the earliest period determine the form and proportions 
of the toe; but as already indicated, the evidence seems to point 
quite as strongly to the alternative possibility, namely, that the 
form of the skeletal elements as first laid down is the result of a 
more or less passive response of cartilage forming cells to the 
influence of surrounding conditions. The relation of brachy- 
dactyly to booting (to be discussed in a later paragraph) adds 
considerable support to the latter interpretation. If this inter- 
pretation is correct, it follows that the early shortening of the 
toe as a whole results in a reduction of the skeletal elements, 
the degree of reduction being directly correlated with the degree 
of shortening, and not improbably passing successively through 
the above described stage till the definitive condition is reached 
on the tenth day or shortly thereafter. 
INTERRELATION OF CHARACTERISTICS 
The relations of brachydactyly and the other hereditary 
characteristics observed in this experiment are indicated in the 
