Not only is this principle embodied in the theory set forth in the article on Rudimentary Organs ("Nature," Volume IX.); but it is more than once hinted at in the "Origin," in the passages where rudimentary organs are said to be more variable than others, because no longer under the restraining influence of Natural Selection.

And still more distinctly is this principle recognised in page 120.
Thus, in sending you the enclosed letter, I do not imagine that I am bringing any novel suggestions under your notice.

As I see that you have already applied the principle in question to the case of artificially-bred structures, I cannot but infer that you have pondered it in connection with naturally-bred structures.

What objection, however, you can have seen to this principle in this latter connection, I am unable to divine; and so I think the best course for me to pursue is the one I adopt--viz., to send you my considerations in full.
In the absence of express information, the most natural inference is that the reason you refuse to entertain the principle in question, is because you show the backward tendency of indiscriminate variability [to be] inadequate to contend with the conservative tendency of long inheritance.

The converse of this is expressed in the words "That the struggle between Natural Selection on the one hand, and the tendency to reversion and variability on the other hand, will in the course of time cease; and that the most abnormally developed organs may be made constant, I see no reason to doubt" ("Origin," page 121).