PRINCIPLES OF BIOLOGY. 
105 
Such variations from the original type would be impos¬ 
sible were it not that distinctive peculiarities, encouraged by 
a natural or artificial selection, have been and are habitually 
transmitted in an equal, in a greater, or in a less degree. In 
the absence of other evidence that which ethnology alone 
furnishes would suffice. 
The illustrations of Heredity are then divided into two 
classes—(1) cases where congenital peculiarities, not traceable 
to any obvious causes, are bequeathed to descendants; (2) 
cases where peculiarities, not congenital, but resulting from 
changes in function during the lives of the individuals 
bequeathing them, are inherited. The necessity of this 
distinction is not very evident, and seems only to confuse, 
as there are many instances of Heredity which it would be 
difficult to place under one class more than the other. There 
are numerous instances of the inheritance of forms modified 
by natural and artificial selection, of the transmission of 
special deformities, of the inheritance of diseases, of pecu¬ 
liarities of skin and of teeth, &c., whilst the direct inheritance 
of an acquired peculiarity is sometimes observable. Mr. Lewes 
gives a case of a puppy that took to begging spontaneously 
(an accomplishment of his mother), and young pointers have 
been noticed to stand and point when first taken into the 
field. 
[The inheritance of an acquired peculiarity can be by no 
means uncommon. Most people can recall instances of an 
inherited twitching of the mouth or eyes, of a peculiar way 
of shaking hands or even of holding a teacup, and of numerous 
other cases of the inheritance of the minutest details of 
habit. Darwin, in the expression of the emotions, gives a 
very singular instance— where a trick of lifting the arm and 
dropping it again with a jerk on to the nose, during sleep, 
was observed to be inherited.] 
As an instance of functional Heredity, Spencer particularly 
cites the musical faculty, the growth of which he explains in 
a remarkably clear and powerful manner. There are two 
modifications of Heredity given on p. 252 ; atavism, and the 
limitation of Heredity by sex, to which we may add what 
Darwin styles a much more important rule than either of 
these, viz., that at whatever age a change appears in the 
parent, it appears in the offspring, e.<j., horns in cattle. 
[Even peculiarities of structure will appear at the same 
age in the offspring as in the parents. In a family known to 
a friend of mine, with several members of two generations, 
one of the eye-teeth has failed to appear till they have reached 
twenty-two or twenty-three years of age.] 
