My dear Mr Darwin

I have examined more than 100 species of all the genera of horned Copridæ & find there is no absolute difference in size between male & female.¹ This conclusion would not perhaps be arrived at, if a good series of each species were not at hand for comparison, as the Copridæ vary unusually in size & ill-developed males smaller than females are very common; but fully developed individuals of both sexes always agree pretty well in size.—

I have looked at a good many Dynastidæ & find the males in some genera a little longer than the females; in bulk they are much greater than the females, owing to horns & their supports, but the difference in length & breadth exclusive of horns, when they come to be measured is not much. The genera Dynastes & Megasoma may be safely quoted as those in which this disparity in size is less subject to doubt.²

I have now no longer a large collection of Orthoptera; but will profit by my next visit to B.M. to notice if there is any sexual difference in colours.³

I have, since I last wrote, re-examined a male house cricket & can confirm my former statement that there is no difference in shape of the two wing cases at the part where the stridulating organs are situated. There is also very little difference in the form of the organ itself on the left & right wing case, one however is probably scored across & the other smooth, I must examine them again under microscope.⁴

We have gained a powerful convert to Darwinianism in M^r Von Kiesenwetter one of the school of learned & rigid systematic Entomologists that has flourished for many years at Berlin. He has written a very lucid & able article, illustrating origin of species by examples in the genus Oreina (chrysomelidæ) in Berlin Entom. Zeitschrift 1867 pt 3–4⁵

Yours sincerely | H W Bates