weight. This seems rather interesting to me. (43/2. On the conclusions
drawn from these researches, see Mr. Platt Ball, "The Effects of Use and
Disuse" (Nature Series), 1890, page 55. With regard to his pigeons, Darwin
wrote, in November 1855: "I love them to that extent that I cannot bear to
kill and skeletonise them.")

P.S.--I do not know whether you will think this worth reading over. I have
worked it out since writing my letter, and tabulate the whole.

21 orders with 1 genus, having 7.95 species (or 4.6?).

29 orders with 2 genera, having 15.05 species on an average.

23 orders each with 3 genera, and these genera include on an average 8.2
species.

20 orders each with 4 genera, and these genera include on an average 12.2
species.

27 orders each with above 50 genera (altogether 4716 genera), and these
genera on an average have 9.97 species.

From this I conclude, whether there be many or few genera in an order, the
number of species in a genus is not much affected; but perhaps when [there
is] only one genus in an order it will be affected, and this will depend
whether the [genus] Erythroxylon be made a family of.


LETTER 44. TO J.D. HOOKER.
Down, April 8th [1856].