The Making of Species 
By inheritance we mean that which an organ- 
ism receives from its parents and other ancestors 
—all the characteristics, whether apparent or 
dormant, it inherits or receives from its parents. 
Professor Thomson’s definition—“<all the qualities 
or characters which have their initial seat, their 
physical basis, in the fertilised egg cell”—seems 
to cover all cases except those where eggs are 
parthenogenetically developed. 
The first fact of heredity which we must notice 
is that inheritance may take several forms. This 
is apparent from what was set forth in the 
chapter dealing with hybrids. 
In considering the phenomena of inheritance 
it is convenient to deal with crosses in which the 
parents do not closely resemble one another, 
because by so doing we are able readily to 
follow the various characters displayed by each 
parent. It may, perhaps, be urged that such 
crosses occur but rarely in nature. This is true. 
But we should bear in mind that any theory 
of inheritance must explain the various facts of 
cross-breeding, so that, from the point of view of 
a theory of inheritance, crosses are as important 
as what we may term normal offspring. As 
inheritance is so much easier to observe in the 
former, it is but natural that we should begin 
with them. Our deductions must, if they be 
valid ones, fit all cases of ordinary inheritance, 
z.é. all cases where the offspring results from the 
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