MEMOIR. ' lxxix 
structure, habits, distribution, and vast antiquity, throws more light 
on the past history of the earth than any other organism ; and, 
therefore, this choice, in the hands of a philosophical naturalist of 
Bates’s stamp, was of the highest advantage to biological science. 
While describing a large number of new species, especially of the 
Geodephaga, or carnivorous land-beetles, he was, as the subjoined 
letter shows, always on the alert to detect subtle modifications, and 
to seek for the causes by which they had been induced. 
HT. W. Bates to Charles Darwin. 
‘©15, WHITEHALL PLACE, S.W., Alarch 22nd, 1865. 
““My DEAR MR. DARWIN,— 
‘‘It gave me great pleasure this morning tosee a letter in your hand- 
writing, showing that you had recovered your previous tolerably good state of 
health. The news will be welcome to all our friends when I tell them. 
‘« Pray do not send your copy of the He/zconzde paper, as I have still a few 
left, and will send one to Mr. Walsh, to whom I am indebted for copies of his 
papers lately arrived. I have read every line of his with great pleasure—just 
a little deadened perhaps by the diffuseness of his style, and want of closeness 
in his otherwise just reasoning. 
“‘T will make use of this opportunity to tell you of a small discovery of 
mine, lately made in working out the species of a very long genus of Longzcorn 
Coleoptera. It is with regard to the abrupt and profound modifications in 
sexual parts between vevy closely allied species. You will perhaps recollect 
my telling you some time ago of a series of dissections of the male organs in 
Chrysometide made by a friend of mine, he having found great differences 
from species to species, and even separated what were previously considered 
to be varieties, on the ground of modifications of these organs. In my 
Longicorns the parts in question are the accessory organs; that is, the 
terminal abdominal segments from which the organ protrudes when necessary. 
The genus is Colobothea—one of those genera of which so many exist in all 
orders in which the species seems to have been endlessly multiplied by nature. 
Nearly all the species can be distinguished by the form of the accessory organs 
in the sexes, and I have found most profound modifications in what would be 
otherwise considered as JocaZ varieties. I have no dcubt whatever that the 
species, on dissemination over a wide area, and breaking up into local varieties, 
undergo modifications of these organs very readily, and that this fact has 
operated greatly in the multiplication of species in nature ; for it is difficult to 
conceive the variously formed males of these closely-allied races to be equally 
adapted to their own females and to the females of their sister races. There 
is a physical obstacle here in the way of amalgamation with the parent or 
sister forms of segregated local varieties or races. I shall publish my notes 
on the subject in the Aznals and Mag. Nat. Hizs?. in the course of my paper 
on Amazons Lomgicorns. 
‘*Yours sincerely, 
He W: BATES?” 
The monograph on the AZantide, to which reference was made 
