138 DOMESTICATED ANIMALS AND PLANTS 
The stooling of grain is a case of branching at the base and 
is a real doubling, as are the four-, five-, or six-leaved clovers. 
The whole matter of doubling is, of course, 
habit proceeding 
from internal 
Fic, 22. A hand- causes to become 
shaped corncob hereditary 
showing a tendency , 
to branching of the Fusingof parts. 
ear, not at all un- Quite the oppo- 
seas alinnde site of doubling is 
the fusing or joining of two parts 
into one. Thus the two kidneys may 
be joined at one end, making the 
horseshoe kidney. A pair of horns 
may be compounded into one. Two 
fingers of the human hand or the 
two toes of the pig! may be united 
into one. 
When unit characters get mis- 
placed. Perhaps the most remarkable 
fact of development and differentia- 
tion is seen when a normal struc- 
ture develops in an abnormal place. 
Thus occasionally a tooth will develop 
in the roof of the mouth, as if the 
germ of it had in some way got 
misplaced but was able to grow in 
the result of an extra cell division at the 
proper point, —an abnormality that is some- 
times hereditary but oftener not, though a 
strong tendency exists for any physiological 
Fic. 23. Compounding of paired 
organs: the two horns of this 
roebuck are united into a single 
beam for a considerable distance, 
but afterwards they separate. — 
After Bateson 
its new place, like a tree that is transplanted. Sometimes the 
eye of an insect will develop not as an eye but as an antenna. 
1 These are the so-called solid- or mule-hoofed hogs. This abnormality 
arises frequently and may be readily propagated, as it happens to be fairly 
hereditary. See “ Principles of Breeding,” pp. 55, 66. 
