302 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
character, D, or the normal recessive character, #, and that equal num- 
bers of D’s and R’s will be produced. Offspring of the crossbreds will 
therefore show these characters in the following ratios: —1D:2 DR:1 R. 
But the character D being dominant, not only the 1 D’s but the 2 DR’s 
will be polydactylous and therefore only one-fourth of the chicks will 
have normal toes. Bateson’s experiments show that this is really the 
case. 
To us the significance of Mendel’s law lies in the fact that a certain 
character may be transmitted pure from generation to generation of 
germ-cells in a latent condition; that is, the character may not appear 
in the structure of the animal, though present in its germ-cells. 
The occurrence in a latent condition of characters which when active 
are dominant may thus explain the constant outcropping of these 
characters, such, for example, as the continual appearance of ‘ rogues,” 
in apparently pure races of plants and in animals which have been 
selectively bred for generations. The appearance of reversionary poly- 
dactylism may be explained in this way. 
Although we know that in the horse, ruminants, swine, and the pes 
of carnivores the extra digits may be of vestigial origin, yet Gegenbaur 
has objected that there is no other evidence of reversion, either in the 
polydactyle extremity or in the general appearance of polydactyle animals. 
We have shown that in polydactyle swine the abnormality is con- 
fined to the manus, and that in most, if not all, cases the extra digits 
represent the development of the normally vestigial pollex. In a third 
of the cases a well-formed digit of two or three phalanges is found, and 
when these conditions are compared with those of the manus of the 
earliest fossil swine, it appears that the two are similar; for a pollex is 
found in the manus of the fossil pig, while in the pes the hallux is 
entirely wanting. In addition to the development of the pollex, other 
modifications were found in the structure of the polydactyle manus, 
which seemed to reproduce a primitive, ancestral condition. We have 
also seen that in most cases of polydactylism in the ox and horse the 
extra digits represent the development of digital parts normally rudi- 
mentary, —a development which might be regarded as due to rever- 
sion, for other parts of the polydactyle member show correlated variations, 
and related fossil ancestors also have the same digits normally developed 
and functional. Moreover, according to recent discoveries in heredity, 
single segregated characters may be inherited, without general modifica- 
tion of the germ-plasm. This has been proved by Bateson and Saunders 
(:02), Castle (03, :03*) and others in agreement with Mendel’s law. 
