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Genital changes are not uncommon in the animal kingdom; 
and the flowering of plants ought to be put in the same 
category. 
Moulting in birds, change of leaf in trees, white winter 
coats of Arctic animals might be called “ periodic or seasonal 
changes.” * 
Changes which are not genital, and not seasonal, such as 
the voluntary change of colour in the chameleon, and in 
certain frogs, and the involuntary change of colour in Man— 
blushing—might be termed simply “occasional” or “‘ temporary” 
changes. 
The above phenomena will suffice as illustrations of what 
I wish to class as otherwise than Variations. The paleonto- 
logical illustrations of the inconstancy, in so many cases, of what 
are termed “species” lead to the assumption that change from 
. generation to generation is the rule, only that it differs in 
degree—in some cases is so slight as to be unappreciable even 
in very extensive genetic séries. In any case I can only define 
as Variation the amount of difference between offspring and 
parent when compared at the same age.t] 
Such Variation may be considered under different headings 
in relation to the the causes by which it is produced. 
I.—Abnormal Variation. This may be subdivided : 
(1) Variation due to disturbance of the economy of the 
parent. This is further divisible into : 
(a) Very extraordinary distwrbance. (Monstrosities, 
and to a less extent supernumary digits and the 
like). 
(b) Less extraordinary disturbance.. (Birth marks and 
any alteration of disposition or features. 
* White hair in man is a senile ontogenetic change. Instances of white hair 
in adolescent man or in children are pathological cases due probably to 
general constitutional debility, or to local disturbance of economy. 
+ In Heterogenesis the number of the generations would also have to be taken 
into account. 
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