Walsh shows that a complete gradation exists between species which are absolutely unaffected by change of food and cases where "difference of food is accompanied by marked and constant differences, either colorational, or structural, or both, in the larva, pupa and imago states."), most of which was new to me.

I have since received your paper on willow-galls; this has been very opportune, as I wanted to learn a little about galls.

There was much in this paper which has interested me extremely, on gradations, etc., and on your "unity of coloration." (186/2.

"Unity of coloration": this expression does not seem to occur in the paper of November 1864, but is discussed at length in that of December 1865, page 209.) This latter subject is nearly new to me, though I collected many years ago some such cases with birds; but what struck me most was when a bird genus inhabits two continents, the two sections sometimes display a somewhat different type of colouring.
I should like to hear whether this does not occur with widely ranging insect-genera?
You may like to hear that Wichura (186/3.

Max Wichura's "Die Bastarde befruchtung im Pflanzenreich, etc:" Breslau 1865.