12 
VAEIATIOH 
Chap. I. 
cats with blue eyes are invariably deaf; colour and 
constitutional peculiarities go together, of which many 
remarkable cases could be given amongst animals and 
plants. From the facts collected by Heusinger, it ap¬ 
pears that white sheep and pigs are differently affected 
from coloured individuals by certain vegetable poisons. 
Hairless dogs have imperfect teeth: long-haired and 
coarse-haired animals are apt to have, as is asserted, long 
or many horns; pigeons with feathered feet have skin 
between their outer toes ; pigeons with short beaks have 
small feet, and those with long beaks large feet. Hence, 
if man goes on selecting, and thus augmenting, any pe¬ 
culiarity, he will almost certainly imconsciously modify 
other parts of the structure, owing to the mysterious 
laws of the correlation of growth. 
The result of the various, quite unknown, or dimly 
seen laws of variation is infinitely complex and diversified. 
It is well worth while carefully to study the several 
treatises published on some of our old cultivated plants, 
as on the hyacinth, potato, even the dahlia, &c.; and it 
is really surprising to note the endless points in structure 
and constitution in which the varieties and sub-varieties 
differ slightly from each other. The whole organisation 
seems to have become plastic, and tends to depart in 
some small degree from that of the parental type. 
Any variation which is not inherited is unimportant 
for us. But the number and diversity of inheritable 
deviations of structure, both those of slight and those of 
considerable physiological importance, is endless. Dr. 
Prosper Lucas’s treatise, in two large volumes, is the 
fullest and the best on this subject. No breeder doubts 
how strong is the tendency to inheritance: like produces 
like is his fundamental belief: doubts have been thrown 
on this principle by theoretical writers alone. When any 
deviation of structure often appears, and we see it in the 
