94 
THE WEEKLY ENTOMOLOGIST. 
theory of uniform Progressive De- 
velopment, I framed the hypothesis 
that species or forms are, and even 
•were mutable, sometimes advancing 
in the scale of organization, semetimes 
retrograding, but always varying, the 
sons from their sires and the sires 
from the patriarchs of their respective 
races. I termed the theory, — The 
Mutability of species or the Mutation 
of Generations. 
Mr. Darwin has dwelt ingeniously 
and satisfactorily upon one cause for 
the alteration of forms of life viz, that 
of the greater fitness to surrounding 
circumstances or the struggle for exis- 
tence of certain slight modifications 
of structure. He has dwelt so exclu- 
sively upon this branch of the great 
subject as almost to lose sight of other 
agencies, for example, the direct 
influences of climate and food, and 
the accumlative effects of those appar- 
ent^ causeless individual variations 
that take place in every generation. 
It is to the latter that I am 
mj self disposed to attribute the greater 
portion of the mutation of forms, or of 
so called species. — 
Let us suppose a separation by an 
intervening ocean, of the two portions 
of a large track of land that were 
previously united and let us further 
suppose the whole of this land to have 
been inhabited at the time of the sep- 
aration, by some race, say, of Geode- 
phagous insects. We will distinguish 
these two non — separated portions of 
land as the eastern, and the western, 
— The generations of the insect in 
question that came into existence after 
the separation of the land, would suc- 
ceed each other as their ancestors had 
previously done each individual differ- 
ing somewhat from the parents, and 
each pair handing down to its progeny 
a structure embracing, what may for 
the sake of explanation be termed the 
hereditary typical form, together with 
a portion of the joint peculiarities of 
the parents themselves, and combined 
with that certain degree of individual 
peculiarity , by which peculiar facies or 
appearances, the new born individual 
would be known to the critical eye 
from all other individuals of the same 
race. The conjoint effect of heredi- 
tary transmission of form, and in- 
dividual peculiarity, will have taken 
in the eastern track one direction, in 
the western probably another. Food, 
climatic conditions of heat and mois- 
ture and natural selection, will have 
acted directly and indirectly in giving 
some bias in respect of form size colour 
and appetites, which, in the indivi- 
duals of either one of the restricted 
districts, will have assumed a degree 
of uniformity owing to the interbeeding 
In the meanwhile, different influences 
have been operating in the other isol- 
ated district and the mutable tendency 
of the race on the ordinary doctrine of 
chances, will almost, as a matter of 
inevitable certainty, have set up a 
bias differing in some respects. It 
thus results, that the longer the per- 
iod of timo during which separation 
has existed, the greater the chance of 
divergence, aud if the races on the 
two separated tracks of land have been 
kept apart for a long period of time, 
