304 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
We have suggested the possibility that a factor in the production of 
polydactylism in man, the cat, and the fowl may be reversion, not to a 
hypothetical heptadactyle ancestor, but to the unmodified minimus, 
pollex or hallux of a not distantly related pentadactyle form. The re- 
acquired structures might prove to be in their germinal characters, like 
those of many neomorphs, so unstable as to lead to variations in the 
next generation, such as polydactylous duplications. 
- We have evidence to show that in man, the cat, and the fowl it is not 
a definite number of extra digits, but a tendency to digital variation and 
duplication which is inherited. In man the minimus may be duplicated 
on all extremities, but to a different degree in each case, and the varia- 
tions may increase in succeeding generations. Thus, Fackenheim (’88) 
cites the case of normal parents whose daughter had a rudimentary sixth 
finger on the ulnar side of each hand. Of her two sons, one had six 
fully developed digits on each hand, the other six digits on all four 
extremities! In another family the first parent observed had six toes on 
each foot. Of eight children three were normal, three had six toes (in 
one case correlated with hare-lip), and two had six fingers ; all the extra 
digits were of symmetrical occurrence. In the three succeeding genera- 
tions extra digits appeared now on the feet, now on the hands, and in two 
cases on all four extremities. In two cases also, seven toes were present 
on one or both feet. 
In a family of cats observed by Poulton (’86) the abnormality ap- 
peared in the third generation (number of extra digits not stated). In 
the fourth generation six toes appeared on all four extremities. In the 
fifth generation there were many individuals with seven toes on all paws, 
and evidences of further duplication in the existence of doubled claws. 
All gradations occurred between the extreme and normal form. This 
condition prevailed up to the ninth generation, although in every case 
the male parent was normal. 
Torrey (:02) describes a similar case in which the offspring of a female 
cat with six toes on the manus and five on the pes showed all gradations 
between the normal and a seven-toed condition. Often in these cats the 
pollex was abnormally long and composed of three phalanges instead of 
two. In all cases digits uv were apparently normal in structure. 
Bateson’s breeding experiments show the same to be the case in the 
polydactylous fowl. On crossing with normal birds all degrees of 
variation are exhibited by the hallux, from simple elongation to 
complete duplications and reduplications. 
These observations bring out the important fact that often no extra 
