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From G. J. Allman   13 April 1872

Athenaeum Club | Pall Mall

April 13, 1872

Dear Mr. Darwin

I have to thank you and the excellent translator very much for the opportunity of reading Malm’s paper on Flat-fish1

My own ignorance of the languages of Scandinavia renders a translation of any portion of its zoolo-literature most acceptable, and when the subject is of such interest as the production of asymmetry in the Pleuronectidæ my obligations for being put in possession of it are especially great.2

Malm’s observations appear to be quite reliable. I think we may regard the retention of the eye on a level with the surface of the head as established by them, and its migration through the skull as untenable.3

I have been reminded by this paper of another point which has doubtless also struck yourself. I refer to the apparent connexion between the stalked condition of the eye in the podophthalmic crustacea and the habits of the animal. I believe that in the Podophthalmia the direction of locomotion in swimming is always retrograde— it certainly is so in the macrourous species, and the connexion between this form of locomotion and the possession of an eye seated on a moveable stalk which enables it to be turned in the direction of the locomotion is obvious.4

The bracyurous forms moreover are macrourous and eminently natatory with retrograde progression in the zoea stage with—if I remember rightly—the eye-stalks excessively developed in this stage.5

I do not think that the sessile-eyed Crustacea are retrograde in their motions. You will perhaps remember how it is with the young barnacle.

Believe me | Ve⁠⟨⁠ry⁠⟩⁠ sincerly yours | ⁠⟨⁠Ge⁠⟩⁠o. J. Allman

I return the translation of Malms paper by this post.

1
CD had evidently sent Allman a manuscript translation of substantial extracts from a Swedish paper on the migration of the eye in flatfishes by August Wilhelm Malm (Malm 1867). The translation, which appears to be in the hand of George Howard Darwin, is in the Darwin Pamphlet Collection–CUL.
2
Pleuronectidae is the family of righteye flounders, so called because adults lie on the sea bottom on their left side, with both eyes on the right side. Malm had studied the development of some species of these fishes from the earliest embryonic stages and noted the gradual movement of the eye as the fish matured. CD discussed Malm’s observations in Origin 6th ed., pp. 186–7.
3
Several authors had suggested that the eye in Pleuronectidae actually moved through the head during development. See Traquair 1865, pp. 263–5, for a review of theories of eye movement.
4
Podophthalmia was formerly the division of stalk-eyed Crustacea that included the orders Decapoda and Stomapoda (Milne-Edwards 1834–40). Locomotion in stalk-eyed Crustacea varies widely and many species are capable of more than one method. Macrurous, or long-bodied, forms of Podophthalmia (all formerly included in the now defunct order Macrura) include lobsters, crayfish, shrimp, and prawns.
5
Brachyurous, or short-bodied, forms of Crustacea include true crabs, porcelain crabs, and squat lobsters. The zoea stage is one or more of the larval stages of crustaceans. True crabs have several zoeal stages, during which the abdomen is still stretched out, so that they resemble macrurous forms.

Please cite as “DCP-LETT-8269,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-8269