lviii MEMOIR. 
and Mr. Darwin will see on reading yours. There is no new view in my line 
of argument—it is the same as Mr. Darwin’s. There is no irreconcilable 
difference, I think, between your view and his, but Mr. Darwin’s seems to 
harmonise best with the facts of variation as gleaned from the distribution 
of closely-allied species and varieties of insects which have come under my 
notice. 
‘‘We all agree that variation exists in nature as a general, perhaps a 
universal, rule. In other words, children are never exactly like each other or 
their parents. Also that natural selection must act, probably on the first, 
surely on an early subsequent generation of a species when it has entered 
under new conditions. 
‘* This is a logical necessity arising from excessive increase and struggle 
for existence. The only debatable point is: do external causes, food and 
climate, influence variation, or is variation a universal condition of reproduc- 
tion, and totally independent of external causes ? 
‘«Mr. Darwin, as I glean from his book, supposes external causes to act in 
three ways :—1. By disturbing the reproductive system of the parents, and 
thereby inducing variability. 2. By promoting use or disuse of organs.. 
3- By acting directly on the constitution in a general or special way. The 
modes of action 2 and 3 of course would be without result if the acquired 
modifications were not transmitted to the offspring. The variations produced 
by No. 1 may be considered as not traceable to the dzvect action of external 
conditions on the parents, as those would be which are due to Nos. 2 and 3. 
‘“‘T think your tendency of opinion is towards the view that variation is not 
brought about, or not at all affected, by any of these three modes. You look 
upon it as a universal condition of reproduction, and compare it as a law with 
gravitation. It is a grand, simple, and beautiful conception. I wish it would 
prove true. I am quite surprised to find how well it suits many facts of the 
apparent formation of new races in nature. I think of it every day in poring 
over my long series of varieties of South American insects, which are all 
carefully ticketed with localities, and have a history to me as being all taken 
and observed by myself; I apply your view and find it to suit well in many 
cases. I have suites of specimens showing the formation of three or more 
distinct races out of one species, and others exhibiting the same process 
half-completed,—z.e., the races are imperfectly segregated, all the intermediate 
gradations existing,—and after repeated examination and long reflection, I 
really do not see the necessity of calling in the action of food or climate to 
explain the process. The local conditions are more favourable to certain 
variations than others; these live and multiply, the intermediates are extin- 
guished. A strong preference of exact counterparts to pair with, and the rarity 
of intermediate grades rendering possible the segregation of races—two or 
more in one locality—though perhaps when the distinct ones were formed they 
were separated by some geographical barrier ; perhaps a slight and unapparent 
one. Nevertheless some facts go to prove that all these three modes of opera- 
tion do prevail. In support of No. 1 comes the important fact so prominently 
brought forward by Mr. Darwin, that the reproductive functions are greatly 
disturbed when a wild species is brought under confinement or cultivation. I 
have distinct proofs from nature that a species is tolerably constant in one 
locality and very inconstant in another ; nay more, exhibiting a tendency to 
