Darwin and Spencer shared some friends, I believe, and Darwin was complementary of Spencer publicly. (Darwin was a genial type who would find something nice to say about nearly anyone. You sometimes have to pay attention to what he doesn't say to discern his real opinion.) The quote is from Darwin's autobiography, which he wrote as a private family document. I believe this passage was cut from the version of the autobiography published by Darwin's son Francis after Charles died, and only restored in the version Nora Barlow published in the 1950's.
Evolution is an integration of matter and concomitant dissipation of motion; during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, through continuous differentiations and integrations; and during which the retained motion undergoes a parallel transformation.
This was parodied by the mathematician Thomas Penyngton Kirkman (often attributed to William James who quoted it) as follows:
Evolution is a change from a nohowish, untalkaboutable all-alikeness, to a somehowish and in-general-talkaboutable not-all-alikeness, by continuous somethingelseifications and sticktogetherations.