From George Gulliver   20 January [1856]1

Mount Alton, Templeogue. [Dublin]

Jan. 20, 1855.

My dear Sir,

It is not singular that the Blood-Discs of different genera of birds should be similar, for widely distinct Families have those corpuscles not distinguishable in size, shape, or structure. When a marked difference of shape occurs it seems to be merely aberrant, as in the Snowy Owl, Passenger Pigeon, Snow-Bunting, Great Butcher Bird, Java Sparrow, &c. And so of certain saurian Reptiles. In my Appendix to Gerber’s Anatomy, 8o. Lond. 1842,2 where the details are fuller than in the Notes to Hewson.3 Indeed, the difference of the corpuscles in the entire class of Birds is not more than may be found in a single Family of Mammals.

All I recollect of the cows and goats that I examined is, that they were those most easily got at in London, & therefore probably the most common ones.4

The measurements of the Dog’s corpuscles 13542th, of the Dingo 13395th, & of the Wolf 13600th of an inch,5 seem much more different in figures than in fact, and no greater than might be obtained by reducing the averages of different sets of measurements of the corpuscles of the very same individual, provided the measurements were not confined to a single dried & invariable specimen of blood.

The measurement in the Dog in Hewson was from a little mongrel. I have examined those of a fox-hound and of other good breeds without noting any marked difference. But the corpuscles of the Fox, after many comparative trials, have always proved very slightly smaller than the corpuscles of the Dog.

I am, | Yours very truly, | George Gulliver.

If you want to see a marked difference of size in the corpuscles of a single family of mammals, compare the comparatively minute corpuscles of the smallest Ruminants or Rodents with the larger corpuscles of the largest species of the same order.

CD annotations

scored pencil
double scored pencil
1
Although the letter is dated 20 January 1855, it seems that this was a mistake. The letter answers queries arising from CD’s reading of Gulliver ed. 1846, a book that he received from Gulliver only after 18 December 1855 (see Correspondence vol. 5, letter to George Gulliver, 18 December [1855]). CD’s copy of Gulliver ed. 1846 is in the Darwin Library–CUL and contains annotations by CD.
2
Gulliver’s appendix to Friedrich Gerber’s anatomy (Gerber 1842) included tables of measurements of the blood corpuscles of mammals and birds.
3
Gulliver ed. 1846 comprises a collection of the writings of the physiologist William Hewson, to which Gulliver added extensive notes relating to his own microscopical observations.
4
CD had marked the measurements of the blood corpuscles of several species and varieties of goats, sheep, and cattle in his copy of Gulliver ed. 1846, p. 238, and wrote in the margin: “What var.”
5
CD had also marked these measurements (Gulliver ed. 1846, p. 238).

Please cite as “DCP-LETT-1632,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-1632