I go on working at sexual selection, and, though never idle, I am able to
do so little work each day that I make very slow progress. I knew from
Azara about the young of the tapir being striped, and about young deer
being spotted (432/2. Fritz Muller's views are discussed in the "Descent
of Man," Edition II., Volume II., page 305.); I have often reflected on
this subject, and know not what to conclude about the loss of the stripes
and spots. From the geographical distribution of the striped and unstriped
species of Equus there seems to be something very mysterious about the loss
of stripes; and I cannot persuade myself that the common ass has lost its
stripes owing to being rendered more conspicuous from having stripes and
thus exposed to danger.


LETTER 433. TO J. JENNER WEIR.

(433/1. Mr. John Jenner Weir, to whom the following letters are addressed,
is frequently quoted in the "Descent of Man" as having supplied Mr. Darwin
with information on a variety of subjects.)

Down, February 27th [1868].

I must thank you for your paper on apterous lepidoptera (433/2. Published
by the West Kent Natural History, Microscopical and Photographic Society,
Greenwich, 1867. Mr. Weir's paper seems chiefly to have interested Mr.
Darwin as affording a good case of gradation in the degree of degradation
of the wings in various species.), which has interested me exceedingly, and
likewise for the very honourable mention which you make of my name. It is
almost a pity that your paper was not published in some Journal in which it
would have had a wider distribution. It contained much that was new to me.
I think the part about the relation of the wings and spiracles and tracheae