of that genus tend to vary?

I have inquired of Sclater and he tells me that he has a considerable
distrust of Gould's information on this point, but that he has not
himself studied humming-birds.

In regard to shells, I have always found that dealers have a positive
prejudice against intermediate forms, and one of the most philosophical
of them, now no more, once confessed to me that it was very much against
his trade interest to give an honest opinion that certain varieties were
not real species, or that certain forms, made distinct genera by some
conchologists, ought not so to rank. Nine-tenths of his customers, if
told that it was not a good genus or good species, would say, "Then I
need not buy it." What they wanted was names, not things. Of course
there are genera in which the species are much better defined than in
others, but you would explain this, as Darwin and Hooker do, by the
greater length of time during which they have existed, or the greater
activity of changes, organic and inorganic, which have taken place in
the region inhabited by the generic or family type in question. The
manufactory of new species has ceased, or nearly so, and in that case I
suppose a variety is more likely to be one of the transitional links
which has not yet been extinguished than the first step towards a new
permanent race or allied species....

Your last letter will be of great use to me. I had cited the case of
beetles recovering from immersion of hours in alcohol from my own
experience, but am glad it strikes you in the same light. McAndrew told
me last night that the littoral shells of the Azores being European, or
rather African, is in favour of a former continental extension, but I
suspect that the floating of seaweed containing their eggs may dispense