To H. G. Bronn [c. 25 February 1860]1
Shoulder-pad. is the thick, almost horny skin on the shoulder
of the wild Boar, which is said to serve as defence to tusks of other boars: I have not examined this myself.—2
Cross & intercross.— There is no difference: I ought not to have used both terms: an English friend has complained of this mistake of mine.—3
Structure anything visible to eye in appearance of parts
Constitution. rate of pulse—period of gestation—length of life—liability to certain diseases—degree of fertility &c &c &c.
Habit—whether diurnal or nocturnal—what kind of food an animal prefers— Habit may, also, be applied to instincts; but it is rather a loose word, often used in English. It differs little from instinct; but would never be applied to the more wonderful instincts. We might say that the owl had nocturnal habits; but instinct impelled it to build its nest.— The optic nerve being fitted to see in the dark we should call a constitutional difference—the great size of eyes a structural difference.—
I am astonished & much pleased that you think the Translation will be ready by May.—4 Most truly do I thank you for the great honour & benefit which you have conferred on me.—
Honoured Sir, Yours very sincerely | C. Darwin
Discusses meaning of various English scientific terms.
Is much pleased that translation [of Origin, 1st German ed.] will be ready by May.